User.cs & ScrollMessageFilter.cs: some tweak to make this 2 file compile on MonoDevelop

But there's other stuff that still need tweak if to be fully compile-able on Mono-Develop,
1) tweak Zero-K.sln file:
"Microsoft Visual Studio Solution File, Format Version 12.00
# Visual Studio 11"
to
"Microsoft Visual Studio Solution File, Format Version 11.00
# Visual Studio 2010"
https://bugzilla.xamarin.com/show_bug.cgi?id=4919

2)put TextToSpeech/SpeechRecognition files into separate module that compile/not-compile if Release/LinuxDebug  build option is used.