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.
Workaround conflict between all-uppercase static and NaN definition.
Revise error message to use phrase "all caps" instead of "uppercase".

This is to clarify that the lint is checking for THIS_THING and not This.
fix tests for check-fast.
fix tests for check-fast.
incoporate suggestion from huonw to move code into lint.rs
Register new snapshots
Obsolete parsing 'loop' as 'continue'
Migrate users of 'loop' to 'continue'

Closes #9467
syntax: remove some dead code.
syntax: indicate an error when a macro ignores trailing tokens.

That is, only a single expression or item gets parsed, so if there are
any extra tokens (e.g. the start of another item/expression) the user
should be told, rather than silently dropping them.

An example:

    macro_rules! foo {
        () => {
            println("hi");
            println("bye);
        }
    }

would expand to just `println("hi")`, which is almost certainly not
what the programmer wanted.

Fixes #8012.
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).
auto merge of #9665 : alexcrichton/rust/snapshot, r=brson

Uses the new snapshots to kill the old `loop` and introduce the new `continue`.
auto merge of #9673 : huonw/rust/macros, r=catamorphism

That is, only a single expression or item gets parsed, so if there are
any extra tokens (e.g. the start of another item/expression) the user
should be told, rather than silently dropping them.

An example:

    macro_rules! foo {
        () => {
            println("hi");
            println("bye);
        }
    }

would expand to just `println("hi")`, which is almost certainly not
what the programmer wanted.

Fixes #8012.