Throw an exception in case of a coroutine re-initialization.
Fix in the muRascal library: create a new array for storing initialized
coroutines; otherwise it leads to a coroutine re-initialization, for
example, in case of enumerators with descendant patterns.
Added tests for enumerators with descendant patterns.
Merge branch 'master' of https://github.com/cwi-swat/rascal.git