Changes regarding environment variables.

I'm working on a non-C# project with monodevelop, where I work with general projects, custom build and run commands and gdb as debugger. I need specific environment variables to be set when the project is executed and this didn't work with the IDE. These two patches fix these bugs.

Similar patches might be used to fix some of the related bugs: https://bugzilla.xamarin.com/buglist.cgi?quicksearch=environment+variables
I can't fix them as I don't use Mono for Android for example (https://bugzilla.xamarin.com/show_bug.cgi?id=4563).