The fallback to latin-1 encoding would not work if the invalid
UTF-8 characters occurred in a skipped branch in an -ifdef/-ifndef.

* egil/maps-compiler-coverage:
  compiler: Do not evaluate map expressions with bad keys
  compiler: Throw 'nomatch' on matching with bad binary keys
  compiler: Variable keys are not allowed in Maps
  compiler: Strengthen Maps warnings tests
  compiler: map_pair cannot be a type clause in v3_life
  compiler: Remove redudant code in v3_codegen
  compiler: Test deep map structure
  compiler: Remove redundant clause in v3_codegen
  compiler: Cover #{ [] => Var } in testcase

Map keys with large (non literal) binary keys must fail.

Even if a binary key is written as a literal the compiler may
choose to make an expression. Emit a warning in those cases
and saying the case will not match.

This is a limitation in current implementation.

Increases coverage.

The pass sys_core_fold did not correctly handle non-matching patterns in code
such as:

    0 = case <<>> of
            <<>> -> 0;
            a -> 1
        end.

Function case_opt_lit/3 is rewritten in two passes to first remove any
non-matching clause and only then potentially remove the related patterns
in each clause.

Reported-by: Ulf Norell

Coverage removed by literals.

* nox/maps-v3_core-lit_vars:
  Properly collect variables in map expressions in v3_core