Fixes for join on maps
Replaced muPrimitive size_array_or_list_... by type-specific size
functions.

This avoids run-time type tests.
Merge branch 'master' of https://github.com/cwi-swat/rascal.git
Added missing when-condition in generated code.
Added some unimplemented operator/type combinations.
Implemented solve statement
Merge branch 'master' of https://github.com/cwi-swat/rascal.git