rustc: check_match::specialize: Make sure the pat_enum/def_struct and pat_struct/def_variant cases are right

[catamorphism]

Former-XXXes say "is this right?"

[catamorphism]

Clearing milestone because it's not obviously blocking anything.

@pcwalton -- what test case(s) would answer the question you asked in a comment ("is this right?")?

[huonw]

Visiting for triage; FIXMEs are still there.