Convert utmp{x}name to int, return useful value. Define _PATH_UTMPX

Convert utmp{x}name to int, return useful value.  Define _PATH_UTMPX

	* syscalls.cc (utmpname): Convert to int.  Return 0 if strdup
	worked, -1 otherwise.
	* include/utmpx.h (_PATH_UTMPX): Define as _PATH_UTMP.
	(utmpxname): Declare as int function.
	* include/sys/utmp.h (utmpname): Ditto.
	* include/cygwin/version.h: Bump API minor version.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>