[CMake] C# support again

[Joshua Jensen]

So, for fun, I was trying to implement C# support through some extra 
.cmake files.  This won't be good enough to work with Visual Studio's 
MSBuild, but I wanted to give it a start.

I ran into an interesting issue.

A simple C# command line appears as follows:

    csc /out:MyApp.exe /target:exe Main.cs App.cs Class1.cs Class2.cs

This is a compile+link all rolled into one.

CMake appears to want the compile and link steps separate.  They aren't 
in the C# compiler.  There are workarounds in .NET 2.0, but they aren't 
as efficient.  For the standard C# compiler to work, all source files 
must be specified on the command line.  If any C# people would like to 
correct me, feel free.

So as far as language bindings go, CMAKE_CSharp_COMPILE_OBJECT and 
CMAKE_CSharp_LINK_EXECUTABLE are technically the same thing.

How do I go about setting this up in CMake?  I need a command like 
CMAKE_CSharp_COMPILE_AND_LINK where all source files can be specified.

Thanks.

Josh