http: Clean up parser usage

http: Clean up parser usage

Move parsers.free(parser) to a single function, which also
nulls all of the various references we hang on them.

Also, move the parser.on* methods out of the closure, so that
there's one shared definition of each, instead of re-defining
for each parser in a spot where they can close over references
to other request-specific objects.

Conflicts:

	lib/http.js