httppeer: refactor how httppeer is created (API)
Previously, we passed a bunch of arguments to httppeer.__init__,
validated them, then possibly constructed a valid instance.
A short while ago, we refactored sshpeer so all the validation and
setup work occurs before the constructor. We introduced a makepeer()
to hold most of this logic.
This commit gives httppeer the same treatment.
As a sign that the previous design was poor, __del__ no longer
conditionally checks for the presence of an attribute that may
not be defined (it is always defined in the new code).
.. api::
httppeer.httppeer.__init__ now takes additional arguments.
Instances should be obtained by calling httppeer.instance()
or httppeer.makepeer() instead.
Differential Revision: https://phab.mercurial-scm.org/D2725