Pop metatable off stack after we have created it
Don't set __metatable
pushlstring( L, STRL( x ) ) -> pushliteral( L, x )
Fix memory leak

Code like

	local parser
	local cbs = { onURL = function() parser:pause() end }
	parser = hp.request( cbs )
	parser:execute()

would leak due to the cycle between parser and cbs, and the reference to
cbs from the registry.

doub in #lua pointed out that in httpCallback/httpDataCallback the
parser userdata was still going to be at stack index 1 and I can use its
fenv/uservalue. thanks doub.