* Move much of ErrorHandler.cs into a partial class in ErrorHandler.tools.cs,
which is referenced by mtouch and mmp (but not our runtime).
* Add ErrorHandler.runtime.cs for runtime-specific bits, including a simpler
version of ErrorHandler.Show. In particular this gets rid of the call to
Environment.Exit, which should never happen at runtime.
* Rename MonoTouchException and MonoMacException to ProductException, which
allows us to remove a lot of ifdefs.
* This required moving Application.LoadSymbols and Target.LoadSymbols to
shared mtouch/mmp code.
Rolf Bjarne Kvinge