[cairo] New per-scaled_font mutex to fix locking bugs

[Vladimir Vukicevic]

Carl Worth wrote:
> For win32, I took a guess and came up with the following
> 
> 	typedef CRITICAL_SECTION cairo_mutex_t;
> 	# define CAIRO_MUTEX_INIT(mutex) InitializeCriticalSection (mutex)
> 	# define CAIRO_MUTEX_FINI(mutex) DeleteCriticalSection (mutex)

These should both be &mutex (the address of the object)

> 	# define CAIRO_MUTEX_NIL_INITIALIZER {}
> 
> The only thing I'm unsure of there is the NIL_INITIALIZER. This is
> only used when initializing the mutex for a nil surface, so the value
> won't ever be looked at, but it does need to compile at least.

Bill pointed out the problems with this; from looking at the windows 
headers, I /think/ { 0 } should work.  I can't try it at the moment 
though, but I'll give it a shot later.

     - Vlad