autoconf: refactor acinclude.m4

autoconf: refactor acinclude.m4

The acinclude.m4 is very large and often requires to be changed for
unrelated commits.  Divy up the large acinclude.m4 into a number of
smaller files to avoid so many contentions and to make the autoconf
system easier to maintain.

This is a non-functional change. Care has been taken preserve the
ordering of the autoconf tests. Except for whitespace, the generated
configure file has not been changed by this refactoring.  This has been
verified with a 'diff -u -w -B' comparison of the generated configure
file before and after applying this commit.

Change-Id: I70e7f846dea0055d00a60a47422aa73bff25c4c6
Reviewed-on: https://gerrit.openafs.org/12842
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>