Correct bug with instantiating _local_context as a thread.local.

_local_context is initialized within the init context method.  This is
causing the thread local to be incorrectly initialized and
consequently get corrupted.
Merge pull request #57 from WebFilings/context_init_error

Correct bug with instantiating _local_context as a thread.local.
Merge branch 'master' of git://github.com/WebFilings/furious
Merge branch 'master' of github.com:johnlockwood-wf/furious into marker-tree