Fix the inverted RUST_LOG filter

RUST_LOG supports regex filtering of log messages with a syntax like
`RUST_LOG=main/foo` to use the regex filter 'foo'. Unfortunately, the
filter was inverted, so `RUST_LOG=main/foo` would actually show all
messages except the ones containing 'foo'.
auto merge of #17331 : kballard/rust/rust_log_pattern_inverted, r=alexcrichton

RUST_LOG supports regex filtering of log messages with a syntax like
`RUST_LOG=main/foo` to use the regex filter 'foo'. Unfortunately, the
filter was inverted, so `RUST_LOG=main/foo` would actually show all
messages except the ones containing 'foo'.
librustc: Implement associated types behind a feature gate.

The implementation essentially desugars during type collection and AST
type conversion time into the parameter scheme we have now. Only fully
qualified names--e.g. `<T as Foo>::Bar`--are supported.
auto merge of #16377 : pcwalton/rust/associated-items, r=nikomatsakis

This is waiting on an RFC, but this basic functionality should be
straightforward. The implementation essentially desugars during type
collection and AST type conversion time into the parameter scheme we
have now.

r? @nikomatsakis