Fix problems in porting to NSK reported by Matthew Woehlke in

Fix problems in porting to NSK reported by Matthew Woehlke in
<http://lists.gnu.org/archive/html/bug-gzip/2006-12/msg00025.html> and
<http://lists.gnu.org/archive/html/bug-gzip/2006-12/msg00027.html>.
* gzip.h: Include <limits.h>, for SSIZE_MAX.
(INBUFSIZE): Don't make it any larger than SSIZE_MAX.
Problem reported by Matthew Woehlke in
<http://lists.gnu.org/archive/html/bug-gzip/2006-11/msg00013.html>.
* gzip.c: Don't include <limits.h>, as gzip.h now does this.
* util.c: Likewise.
* gzip.c (main): Set exiting_signal before installing signal handlers.
(install_signal_handlers): Don't set exiting_signal here.  This
fixes a C99ism.
* zip.c: Include timespec.h, for time_stamp type.