Added MacOS versions of FreeImage.NET

Added a universal Assembly which uses non unicode api
calls when loading files. This should work on all platforms
as the unicode versions only worked on windows.

The libfreeimage.dylib files were sourced from brew and
are universal binaries and as such will work on both
x64 and x86 system.
Fixed the Diff so its the right way round
Merge pull request #29 from dellis1972/master

Added MacOS versions of FreeImage.NET