MaskComBinar remembers deleted masks (and keeps memory allocated)

[GoogleCodeExporter]

What steps will reproduce the problem?
1. A mask is deleted
2. A mask with an identical name as the deleted mask is added

What is the expected output? What do you see instead?
The newly created / loaded mask should be displayed, but instead the previous 
mask is displayed. 
This is probably because the original surface is not removed when the mask
is deleted.

Original issue reported on code.google.com by [email protected] on 16 Feb 2012 at 9:57