Fix size test in PSX Doom image format detection
Merge pull request #38 from iid/master

Fix #37 (Doom picture misidentified as Doom PSX picture)
- Changed vs2012 project to target v110_xp
- Ignore gfx offset spin control change events when offsets are changed via other means. Should fix #15
- Hide next/prev image buttons on gfx entry panel if the entry only contains 1 image
- Fix #33 and a few other similar issues
- Update affected map geometry on undo/redo moving vertices, fixes #32