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

Replace most calls to krb5_set_error_message with k5_setmsg for
brevity.  Leave alone plugin sources where we don't include k5-int.h
(mostly PKINIT).

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.

Locking and unlocking a non-recursive mutex is a simple memory
operation and should not fail on any reasonable platform with correct
usage.  A pthread mutex can return EDEADLK on lock or EPERM on unlock,
or EINVAL if the mutex is uninitialized, but all of these conditions
would reflect serious bugs in the calling code.

Change the k5_mutex_lock and k5_mutex_unlock wrappers to return void
and adjust all call sites.  Propagate this change through
k5_cc_mutex_lock and k5_cc_mutex_unlock as well.

Rename the krb5int_buf_ family of functions to use the k5_ prefix for
brevity.  Reformat some k5buf implementation code to match current
practices.

Add k5-int.h static functions to duplicate byte ranges, optionally
with a trailing zero byte, and set an error code like k5alloc does.
Use them where they would shorten existing code.

Mostly this gets rid of the trailing space on line 2 after
bb76891f5386526bdf91bc790c614fc9296cb5fa.