Workarounds for a bug in 64 bit versions of Mono which stops OpenRA building

[happy0@gamma OpenRA]$ make
CSC OpenRA.Game.exe
OpenRA.Game/Exts.cs(378,6): error CS1525: Unexpected symbol `?'
Compilation failed: 1 error(s), 0 warnings
Makefile:249: recipe for target 'OpenRA.Game.exe' failed
make: *** [OpenRA.Game.exe] Error 1
[happy0@gamma OpenRA]$ mono -V
Mono JIT compiler version 3.10.0 (tarball Mon Oct  6 20:46:04 UTC 2014)

Mono bug report : https://bugzilla.xamarin.com/show_bug.cgi?id=23319 (it appears to have been resolved in master so shouldn't be present in future versions of Mono)

Mono 3.10 seems to be unhappy with ternary statements of a certain format, so I desugared those breaking the build into if statements (and OpenRA subsequently built.)

I wasn't sure whether you would accept this pull request, since I'm not sure whether changing code to work around compiler bugs is even a good idea, but I thought I'd give you guys the option anyway. Arguably the code is a bit more readable this way anyway :P. Up to you!

This issue also affects 32 bit mono, so you should drop the 64 bit mention.