Pre-compiling regex that removes control characters.

Given that this regex might be used a lot in the lifetime of a given server (each request that uses get_argument for unicode strings) it seems sensible to store the compiled version of the regex.
Handle non-ascii data in logged exceptions like in the main message.

Closes #675
Merge commit 'e3f8aa' from heynemann/master

Closes #677
Clarify docstring of IOLoop.stop.

The mention of "after the current iteration" was meant to emphasize that the
stop was not instantaneous, but it could have also been read as a guarantee
that one more poll call would take place.

Closes #672.
Escape non-ascii bytes in tracebacks line-by-line instead of all at once.

Previously if there were any bytes that needed escaping, the newlines
would get escaped as well, ruining the message formatting.

Closes #675 (again)
Add a workaround for a bug in the latest version of libcurl
Make LogTrapTestCase fail more gracefully in unknown logging configurations.

This allows LogTrapTestCases to be run under nose, which does its own
log buffering.

Closes #674
Merge remote-tracking branch 'upstream/master'