Change internal gid datatype from __gid16_t to __gid32_t

	Change internal gid datatype from __gid16_t to __gid32_t
	throughout.
	* cygwin.din: Export new symbols chown32, fchown32, getegid32,
	getgid32, getgrgid32, getgrnam32, getgroups32, initgroups32, lchown32,
	setgid32, setegid32, getgrent32.
	* grp.cc (grp32togrp16): New static function.
	(getgrgid32): New function.
	(getgrnam32): Ditto.
	(getgrent32): Ditto.
	(getgroups32): Change name of internal function from getgroups.
	(getgroups32): New function.
	(initgroups32): Ditto.
	* syscalls.cc (chown32): Ditto.
	(lchown32): Ditto.
	(fchown32): Ditto.
	(setegid32): Ditto.
	(setgid32): Ditto.
	* uinfo.cc (getgid32): Ditto.
	(getegid32): Ditto.
	* include/cygwin/grp.h: Remove declaration of getgrgid() and getgrnam().
	Declare getgrgid32() and getgrnam32() instead.  Declare getgid32().