Change the appliance so PATH includes common directories.  Thus
we don't need to hard-code paths to binaries (eg. "/sbin/fdisk")
everywhere.

The problem is that mkfs was making an ext2 filesystem,
which later we were checking with e4fsck.  e4fsck corrects
an "error" on the filesystem:
  /dev/VG/LV: Adding dirhash hint to filesystem.
e4fsck returns 1 (errors corrected) which we were interpreting
as an error return.

The RPC stubs already prefix the command name to error messages.
The daemon doesn't have to do this.  As a (small) benefit this also
makes the daemon slightly smaller.

Code in the daemon such as:

  if (argv[0] == NULL) {
    reply_with_error ("passed an empty list");
    return NULL;
  }

now results in error messages like this:

  ><fs> command ""
  libguestfs: error: command: passed an empty list

(whereas previously you would have seen ..command: command:..)

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'

* 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.

On RHEL 5, mke2fs is ancient, and there is a non-standard "mke4fs"
binary which acts like the more recent mke2fs on Fedora.  Since there
are several annoyances and actual bugs in the ancient RHEL 5 mke2fs,
use mke4fs instead if it's available.