remove workaround for very old Mono bugs
officially bump the required Mono version to stable 2.10.X

closes #2597
those old Ubuntu/Compiz versions are not maintained anymore
Binary patch the OSX mono check to 2.10.0 for x86.
Remove obsolete ppc arch from OSX launcher.
Update the mono install prompt text too.
Update source code to match.
bump mono runtime version to 2.10 for Debian
Merge pull request #3739 from Mailaender/legacy-mono-eos

Dropped support for ancient Mono versions