[GEP-23] Future parser fails on lambda local variables
Fix typo in error message concerning unsupported lambda
[GEP-22] Complains about uninitialized variables in lambda

This commit prevents variables declared as lambda arguments to be
disqualified as lhs in assignment expressions by adding a trap for
lambda expressions in the iteration of the parent chain. This to
prevent that a potential assignment of the lambda result disqualifies
the lambda argument list.