Add support for parsing --setenv from bundler arguments and passing them to
dotnet-linker so that the environment variables can be baked into the app at
launch (like they would be for mtouch/mmp).
* Change the parsing code slightly, to make it easier to parse other arguments
(coming soon).
* Add the parsing task to Xamarin.Mac projects, and use it there as well. The
parsed result isn't used yet, but it will be soon.
* Unify a few related MSBuild properties (MtouchNoSymbolStrip and
MtouchNoDSymUtil).
Rolf Bjarne Kvinge