previously, a connection could be created based on request options. The
main problem is that requests may have special headers, which would make
them assign its own connection due to the headers mismatch in headers to
the already open connection to the same origin. This, in certain
scenarios, coupled with the persistent plugin, cascades into multiple
connections to the same host which are never closed.

This fix ensures that connection initial options comes from the session.
This way, it'll never change (as connections exhaust). Alongside that,
matching headers was relaxed to only take into account headers which the
original connection knows, special request headers will then opt out
from this.