Make the magic and location arguments to the error-checking-mutex

Make the magic and location arguments to the error-checking-mutex

2006-05-10  Sebastian Wilhelmi  <wilhelmi@google.com>

	* glib/gthread.h, gthread/gthread-impl.c: Make the magic and
	location arguments to the error-checking-mutex functions const and
	do not write to them, as we might not own them. Clean up the
	error-checking-mutex code quite a bit. (#335198, Chris Wilson)