move Pak.cs to the correct directory

case-sensitive OS require it to compile using MonoDevelop
Update CHANGELOG for recent ra oil derrick change
Merge pull request #4242 from ScottNZ/bleed

Update CHANGELOG for recent ra oil derrick change
Merge pull request #4228 from Mailaender/pak-folder-fix

Moved Pak.cs to the correct directory
don't crash when the tileset can not be found

fixes #3033