Include autoconf.h (either directly or via proxy) before system
headers, so that feature test macros defined there can affect the
system namespace.  Where include order was changed, eliminate some
redundant or unnecessary includes.

ticket: 7961

Remove code to set or reference the length fields of socket addresses
(sa_len/sin_len/sin6_len), since they aren't portable and setting them
is not required.  Remove autoconf tests for those fields which are no
longer used or which were never used.

There is one exception: in localaddr.c, we still neeed to reference
sa_len for the definition of ifreq_size on platforms which have
sa_len.  Leave that behind, along with the autoconf test which defines
SA_LEN.

In socket-utils.h, replace the socklen macro with an inline function
sa_socklen which always uses the address family, even on platforms
with the sa_len sockaddr field.  This removes the need to set sa_len
in socket addresses we construct.

When the normal (acceptor) keytab is being used to obtain initial
credentials, it is reasonable to use the default hostbased service
principal (host/fully.qualified.localhost.domain) when no client
principal is given.  This behavior is not very reasonable when
the default client keytab is being used, as host/ credentials are
not normally client credentials.

Make kinit -i match up with the GSS-API behavior when client keytabs
are in use, using the name of the first entry in the keytab when
no name is explicitly given.

ticket: 7892

Add an adapted version of extended_com_err_fn from kinit to klist and
use it.  In do_ccache(), rely on the ccache type to set a reasonable
message if krb5_cc_set_flags() or krb5_cc_get_principal() fails due to
a nonexistent or unreadable ccache, and don't confuse the user with
the name of the ccache operation that failed.

ticket: 7809

If kinit chooses a client principal based on anything other than the
current default ccache's principal name, apply collection rules if
possible.  When applying collection rules, if we don't find an
existing cache for the client principal, use the default cache if it
is uninitialized, instead of creating a new one.

ticket: 7689

When walking the cache, if we skip a cred because it's a config entry,
make sure to free it.  Also free the result of krb5_cc_get_principal.
Based on a patch from Nalin Dahyabhai.

Provide default values in pre.in for PROG_LIBPATH, PROG_RPATH,
SHLIB_DIRS, SHLIB_RDIRS, and STOBJLISTS so that they don't have to be
specified in the common case.  Rename KRB5_RUN_ENV and KRB5_RUN_VARS
to RUN_SETUP (already the most commonly used name) and RUN_VARS.  Make
sure to use DEFINES for local defines (not DEFS).  Remove some other
unnecessary makefile content.

The string "KDB:" has four characters, not three; check for all four
of them.

[ghudson@mit.edu: commit message]

ticket: 7636