This large commit changes the generator so that optional arguments
can be supported for functions.

The model for arguments (known as the "style") is changed from
(ret, args) to (ret, args, optargs) where optargs is a more limited
list of arguments.

One function has been added which takes optional arguments, it is
"add-drive-opts", modelled as:

  (RErr, [String "filename"], #required
         [Bool "readonly"; String "format"; String "iface"]) #optional

Note that this function is processed in the library (does not go over
the RPC protocol to the daemon).  This has allowed us to simplify
the current implementation by omitting changes related to RPC or the
daemon, although we plan to add these at some point in the future.

From C this function can be called in 3 different ways as in these
examples:

  guestfs_add_drive_opts (g, filename,
                          GUESTFS_ADD_DRIVE_OPTS_READONLY, 1,
			  GUESTFS_ADD_DRIVE_OPTS_FORMAT, "raw",
                          -1);

(the argument(s) between 'filename' and '-1' are the optional ones).

  guestfs_add_drive_opts_va (g, filename, args);

where 'args' is a va_list.  This works like the first version.

  struct guestfs_add_drive_opts_argv optargs = {
    .bitmask = GUESTFS_ADD_DRIVE_OPTS_READONLY_BITMASK,
    .readonly = 1,
  }
  guestfs_add_drive_opts_argv (g, filename, &optargs);

This last form lets you construct lists of optional arguments, and
is used by guestfish and the language bindings.

In guestfish optional arguments are used like this:

  add-drive-opts filename readonly:true

In OCaml these are mapped naturally to OCaml optional arguments, eg:

  g#add_drive_opts ~readonly:true filename;

In Perl these are mapped to extra arguments, eg:

  $g->add_drive_opts ($filename, readonly => 1);

In Python these are mapped to optional arguments, eg:

  g.add_drive_opts ("file", readonly = 1, format = "qcow2")

In Ruby these are mapped to a final hash argument, eg:

  g.add_drive_opts("file", {})
  g.add_drive_opts("file", :readonly => 1)
  g.add_drive_opts("file", :readonly => 1, :iface => "virtio")

In PHP these are mapped to extra parameters.  This is not quite
accurate since you cannot omit arbitrary optional parameters, but
there's not much than can be done within the limitations of PHP
as a language.

Unimplemented in: Haskell, C#, Java.

Convert all uses automatically, via these two commands:
git grep -l '\<exit *(1)' \
  | grep -vEf .x-sc_prohibit_magic_number_exit \
  | xargs --no-run-if-empty \
    perl -pi -e 's/\b(exit ?)\(1\)/$1(EXIT_FAILURE)/'
git grep -l '\<exit *(0)' \
  | grep -vEf .x-sc_prohibit_magic_number_exit \
  | xargs --no-run-if-empty \
  perl -pi -e 's/\b(exit ?)\(0\)/$1(EXIT_SUCCESS)/'
* .x-sc_prohibit_magic_number_exit: New file.

Edit (RWMJ): Don't change Java code.

This change adds an explicit dependency on generator.ml for every file it
generates, except java files. Java is left for another time because it's
considerably trickier.

It also adds a build rule for src/libguestfs.la so it can be rebuilt as required
from other directories.

It does this by creating a top level make file, subdir-rules.mk, which can be
included from sub-directories. sub-directories need to define 'generator_built'
to include local files which are built by generator.ml, and they will be updated
automatically.

This fixes parallel make, and will automatically re-create generated files when
make is run from any directory.

It also fixes the problem which efad4f53 was targetting. Specifically,
src/guestfs_protocol.(c|h) had an erroneous dependency on stamp-generator, and
therefore generator.ml, despite not being directly created by it. This caused
them to be recreated every time generator.ml ran rather than only when
src/guestfs_protocol.x was updated, which cascaded into a daemon and therefore
appliance update.

This patch also changes the contents of the distribution tarball by including
files created by rpcgen.

git grep -l 'strcmp *([^=]*== *0'|xargs \
  perl -pi -e 's/\bstrcmp( *\(.*?\)) *== *0/STREQ$1/g'

git grep -l 'strncmp *([^=]*== *0'|xargs \
  perl -pi -e 's/\bstrncmp( *\(.*?\)) *== *0\b/STREQLEN$1/g'

git grep -l 'strncmp *([^=]*!= *0'|xargs \
  perl -pi -e 's/\bstrncmp( *\(.*?\)) *!= *0/STRNEQLEN$1/g'

Since this program is just an example, it shouldn't require
the Gnulib c-ctype functions.

* cfg.mk (disable_temporarily): Don't disable sc_avoid_ctype_macros.
* fish/tilde.c: Remove unnecessary inclusion of ctype.h.
* bootstrap: Add gnulib's c-ctype module to the list.
* daemon/m4/gnulib-cache.m4: Likewise.
* daemon/ext2.c: Include "c-ctype.h", not <ctype.h>.
Use c_isspace, etc, rather than isspace.
* daemon/guestfsd.c: Likewise.
* daemon/lvm.c: Likewise.
* daemon/proto.c: Likewise.
* fish/fish.c: Likewise.
* fish/tilde.c: Likewise.
* src/generator.ml: Likewise.
* src/guestfs.c: Likewise.
* examples/to-xml.c: Likewise.
* examples/Makefile.am (to_xml_CPPFLAGS): Add -I$(top_srcdir)/gnulib/lib
so inclusion of "c-ctype.h" works.
(to_xml_CPPFLAGS): Rename from to_xml_CFLAGS.

This commit changes guestfs_launch so that it both launches
the appliance and waits until it is ready (ie. the daemon communicates
back to us).

Since we removed the pretence that we could implement a low-level
asynchronous API, the need to call launch() followed by wait_ready()
has looked a bit silly.

Now guestfs_wait_ready() is basically a no-op.  It is left in the
API for backwards compatibility.  Any calls to guestfs_wait_ready()
can be removed from client code.