Remove the longest-match logic in module-name matching for logging

[pcwalton]

It's rather confusing.

[bblum]

nominating for feature-complete milestone

[huonw]

Triage 2013-08-05: I believe this is still around; a minor part of #3309.

[graydon]

just a bug, removing milestone/nomination.

[alexcrichton]

I would want to nominate this, but it appears that it was previously deemed as just a bug. To me it's not clear that this should be removed right-out but perhaps replaced with something, and if it's replaced with something with what?

I find it kinda convenient to have prefix matching, but then again I also haven't attempted to get the logs of rustc::middle::ty only get inundated with rustc::middle:typeck

[alexcrichton]

cc @nick29581, could this move to https://github.com/rust-lang/log?

[rust-highfive]

This issue has been moved to the RFCs repo: rust-lang/log#6