Lock when changing album art

If we lock, then we prevent the possibility that multiple threads will
attempt to change the art at the same time.  We hold the lock until
after the resize for the same reason.

ocarina/image.py

@@ -2,6 +2,10 @@
 import libsaria
 import gtk
 
+from libsaria import threads
+
+lock   = threads.get_mutex("album_art")
+
 class Image(gtk.Image):
 	def __init__(self):
 		gtk.Image.__init__(self)
@@ -34,11 +38,13 @@ class AlbumArt(Image):
 		self.file = "images/ocarina.png"
 
 	def set(self, file=None):
+		lock.acquire()
 		if file != None:
 			self.file = file
 		self.set_from_file(self.file)
 		self.set_height(64)
 		self.show()
+		lock.release()
 
 	def set_height(self, new_h):
 		size = self.size_request()