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

This only help a bit if someone tries soo hard to compile on MonoDevelop and use "LinuxDebug" build

There's other stuff that they will still need tweak if to compile on Mono-Develop,
1) tweak Zero-K.sln file header:
"Microsoft Visual Studio Solution File, Format Version 12.00
\# Visual Studio 11"
into
"Microsoft Visual Studio Solution File, Format Version 11.00
\# Visual Studio 2010"
https://bugzilla.xamarin.com/show_bug.cgi?id=4919

2)manually exclude TextToSpeech/SpeechRecognition files or put them  into separate module that compile/not-compile if Release/LinuxDebug  build option is used.

3) remove this line from ZeroKLobby.csproj : https://github.com/ZeroK-RTS/Zero-K-Infrastructure/blob/master/ZeroKLobby/ZeroKLobby.csproj#L8 (what this do?)
" \<ProjectGuid\>{AA5F8640-FBBC-4007-9589-6C7CD26D4867}\</ProjectGuid\> " ?