Rename g_read_link() to g_file_read_link() to better match the remaining

Rename g_read_link() to g_file_read_link() to better match the remaining

	* glib/gfileutils.[hc]: Rename g_read_link() to g_file_read_link() to better match the remaining file
	utilities in the g_file_ namespace and to better separate it from readlink(). This is hopefully no problem
	as the function is just 2 days old.