Wrong grammar for `match`.

[steffahn]

In the grammar for match, i.e. for the nonterminal MatchExpression, in MatchArms the right-hand side of the non-last arms only allows skipping the , for BlockExpression. However it seems to be the case that any ExpressionWithBlock works without the ,. Is this correct?

Furthermore, currently the case of a BlockExpression followed by , matches both alternatives of the BlockExpression ,? | Expression ,. Perhaps a nicer rule would use ExpressionWithoutBlock , | ExpressionWithBlock ,?, in effect being similar to my proposed rule for ExpressionStatement in #773, but with comma instead of semicolon.

Finally, in the last arm, the BlockExpression | Expression part seems a bit redundant as a BlockExpression is an Expression.

[ehuss]

This all sounds like good changes to me.