Windows support bits from Steve Chamberlain <sac@slash.cygnus.com>.

	Windows support bits from Steve Chamberlain <sac@slash.cygnus.com>.
	* defs.h: Don't declare strchr and friends if WIN32.
	(DIRNAME_SEPARATOR): Move here from source.c.
	(SLASH_P, SLASH_CHAR, SLASH_STRING, ROOTED_P): New macros,
	symbolic definitions for filename bits.
	* top.c (cd_command): Use these.
	* source.c (mod_path, openp): Ditto.
	* terminal.h: Disable termio/sgtty definitions if WIN32.
	* findvar.c (registers_changed): Call registers_changed_hook
	if it is defined.