* configure.in: Call AC_TYPE_MODE_T.
(AC_CHECK_HEADERS): Add libc.h, to get more prototypes on the
NeXT. Put header file list in alphabetical order.
* configure, scmconfig.h.in: Regenerated.
* filesys.c [HAVE_LIBC_H]: #include <libc.h>.
* acconfig.h: New file, providing documentation for the CPP
symbols defined in configure.in
* acconfig-1.5.h: Removed; superceded by the above.
