gorilla/context - don't leave old requests in the map
Changing clearhandler to be added to the middleware rather than called outside of it
Merge branch 'cryptix-master'

As cryptix notes, unless context.ClearHandler is called on anything
using gorilla/context, old requests can remain in the map.

We fix this problem by applying ClearHandler outside of any calls to
context (i.e., by adding the handler to the middleware after all of
the other middleware that might use the context).