Created a failing test

So it fails playback when doing things concurrently using the
AsyncHttpClient from Apache Http Components.

This is similar to the behavior I found when I ran the proxy standalone.
Of note is that it doesn't seem to fail if the tape is READ_WRITE. Will
have to add a test to demonstrate that as well, then refactor all the
duplicated code out.
Modified the test to do both tape modes

Now it's a bit more configurable, and no repeat code. yay
Adding deadlocked thread count
Seems I probably made a mistake here. That error message is wrong
a small change or two to the BetamaxFilters

Mostly a TODO note with regards to how to handle the CONNECT part.

And then using a ProxyUtils method that was mentioned in the
littleproxy javadocs instead of doing the same check ourselves. It reads
a bit nicer.
Updating the concurrency tests to prove they work
Merge pull request #129 from dkowis/concurrency_tests

Concurrency tests