Merge pull request #83 from Gaerzi/master

Sync with my fork.
Fixed more undo/redo problems in the map editor
Merge branch 'master' of https://github.com/sirjuddington/SLADE.git
Update VS2012 solution
Fixed saving of maps within zip/pk3 archives
Merge branch 'master' of https://github.com/sirjuddington/SLADE