Include an affinity token by default as GET `a`

An additional token should now be sent with
every request as GET variable `a` by default.

Per #35 a unique token should be created per instance of
BCSocket, allowing a correctly configured load balancer to
consistently route all requests from the same BCSocket instance
to the same Browserchannel server.
[closure-library#df47692b1bac] compile 6880f412c9

Compiled Using
--------------
- [Closure Library] `df47692b1bac` with included closure-terminate-fixes-r2519.patch applied
- [Closure Compiler] `v20140110`

Notes
-----
A newer closure-library exists but causes #34 (closure-library#83c6a0b97bd1)

[Closure Library]: https://code.google.com/p/closure-library/source/detail?r=df47692b1bacd494548a3b00b150d9f6a428d58a
[Closure Compiler]: http://dl.google.com/closure-compiler/compiler-20140110.tar.gz