configure.in: Check for unistd.h as well.

0
	* configure.in: Check for unistd.h as well.
	* configure: Rebuild.
	* config.in: Rebuild.
	* getpagesize.c (GNU_OUR_PAGESIZE): Use sysconf only if _SC_PAGESIZE
	is defined in unistd.h. Reformat conditional block for easier reading.
	* config.table (shared): Default to no if ${enable_shared}
	is unset or empty; this logic is used by the toplevel
	configure scripts, too.

From-SVN: r19924