Undo VS2010/VS2012 project split and use conditional elements when neede...

There is no need to split projects for VS2010/2012. They are supposed to [be](http://msdn.microsoft.com/library/hh266747) [compatible](http://msdn.microsoft.com/library/hh690665).

The only tricky part is conditional choice of toolset and import libraries, but this can be easily achieved by taking advantage of `$(VisualStudioVersion)` variable.

Attached patch merges back all projects and solutions. I've confirmed that it compiles with VS2012 and VS2010sp1.