Added missing is_defined test in MATCH_VAR
Reduce comparison on rel to comparison on set.
Fixed error in map_greater_map
Handling of !:= inside all.
Fixed map_field_project
Fixed subscript on empty rel/lrel
Progress with testing: at 93%
Added tests for relational operators on rel and lrel.
Undone lowering of rel/lrel to set/list from 

This was done in commit 4df20e88d7d434ebe78a4d1faa0401115f80687d to
implement comparison operators on rel and lrel. These have now been
added to RascalPrimitive
Removed print statements
Extended error message in addProduction
Removed is_defined check from MATCH_TYPED_VAR
Fixes #463. Partly addresses issue #460 by making FunctionInstance and
OverloadedFunctionInstance an ICallableValue.
Added tests related to issues #460 and #463.
Merge branches 'master' and 'muAnd-muOr' of https://github.com/cwi-swat/rascal into muAnd-muOr