Bug 548967 - 1 bit mutex lock

Add support for a mutex lock that consumes only one bit of storage
inside of an integer on systems that support futexes.  Futex is emulated
(at a higher cost) on systems that don't have it -- but only in the
contended case.

docs/reference/glib/glib-sections.txt

@@ -660,6 +660,11 @@ g_once
 g_once_init_enter
 g_once_init_leave
 
+<SUBSECTION>
+g_bit_lock
+g_bit_trylock
+g_bit_unlock
+
 <SUBSECTION Private>
 G_THREAD_ECF
 G_THREAD_CF