Fixed bug in C# project algorithm

I hate assumed that something in the solution file was the project
path... which was not the project path. This caused a bug when the
project path was different than the project name (which seems to be what
the field actually is).
Fixed a known limitation in the C# algorithm

It did not support opening files which were directly under the project's
directory; it only supported opening files in sub-projects. This should
fix that.