Update from SVN (r1412)
Some fixes/additions thanks to Dustin Parker:
- Added ability to copy/paste line properties
- Implemented grid sizes and snapping for non-integral grid
- Fix crash on right click during line draw
- Improved map architecture copy/paste
Added check for map modification + save prompt on closing the map editor window
Set correct locale when writing UDMF maps (so that floating point numbers are written in the correct format)