Closed-over environments are now rebound when copied into extending module (fixes #195).
Changed/added utities that return a set of messages.
Major revision of TTL:
- Added test types
- Improved reporting

Nonetheless, still much to do.
Tightened rules for typing intersections
Improved messages for subtraction rules plus fixed some bugs, also turned back on custom type printing to improve type display in error messages
Fixes bug caused by overloading constructors with keyword parameters
Fix in subtyping of two overloaded function types.
Added rascal types as an option to the random type generator; added lub
and glb tests for the rascal types.
Merge branches 'add-glb' and 'master' of https://github.com/cwi-swat/rascal into add-glb