Add new lint: non_uppercase_pattern_statics, for #7526.

This tries to warn about code like:
    ```rust
    match (0,0) {
        (0, aha) => { ... },
        ...
    }
    ```
where `aha` is actually a static constant, not a binding.
Throwing in another interesting test case: There is no need to warn
about constants that are (non-trivial) paths rather than just
identifiers, regardless of what case their characters are.
Fix typo in comment.
Expanded test to clarify that the constants *are* matching when they should.
auto merge of #9638 : pnkfelix/rust/fsk-issue7526-attempt-to-catch-nonuc-statics-in-match-patterns, r=alexcrichton

r? anyone

Address scariest part of #7526 by adding a new more specific lint (that is set to warn by default, rather than allow).