portage is missing Mono Debugger, that is a dependency of dev-util/monodevelop (see http://bugs.gentoo.org/show_bug.cgi?id=132457 ) attached there is the ebuild.
Created attachment 96292 [details] dev-dotnet/monodebugger
Created attachment 96296 [details] dev-dotnet/monodebugger more recent version
*** This bug has been marked as a duplicate of bug 96652 ***