Since we already have the define ISC_STATUS_LENGTH for the the length of
the status vector, we should use it! Replaced 'status[20]' with
'status[ISC_STATUS_LENGTH]'.
Replaced the different symbolic names for the maximum length of a path
(MAX_PATH, MAX_PATH_LENGTH, MAXPATHLEN) with one uniq symbol MAXPATHLEN.
o autoconf v2.53 and later is now required to generate configure
(sorry, but it makes many tasks easier)
o improved tests for mmap, socklen_t and offt_64
o added tests for atexit, on_exit, (v)fork, set(p)grp, setpgid and flock
o added test for the keyword 'volatile'
o fixed errors in configure.in
o updated config.h.in and autoconfig_msvc.h (the latter may be incorrect)
o replaced VOLATILE by volatile
o removed SETPGRP and ATEXIT
o replaced NO_FLOCK by HAVE_FLOCK
o SIG_FPTR cleanup
o vfork cleanup
