android fixes for compatibility of cordova 3.0.x

First of all thanks for iOS changes, because https://github.com/alunny/ChildBrowser wouldn't work without them.

this pull request fixes android issues, including `exec() call to unknown plugin` and compile problems with 3.0.x. I'll update your pull request ( https://github.com/alunny/ChildBrowser/pull/36 ) to include a link to this one to notify alunny.