This reduces the supported `zope.conf` directives when run under WSGI.
In particular directives related to ZServer and zopectl and those
changing sys.path are not supported.

Most code related to temp_folder was already removed in 4.0a1.

If Zope is run as a WSGI app, this avoids doing any ZServer related work.

This avoids various import dependencies between the Startup code
and ZServer/webdav.

Based on https://gist.github.com/optilude/1548061.

This serves the same purpose as `egg:paste#httpexceptions`, but
recognizes exceptions derived from `zExceptions.HTTPException`.