Fix error dispatching webhook with auth credentials
The error was:
AttributeError: 'SplitResult' object has no attribute 'params'

The 5-tuple used for rebuilding the URL was missing the fragment element instead.

Log webhook server responses on error
If the exception from urlopen represents an HTTP response, then the included

information may be useful to the site admin in troubleshooting.

Always send Authorization header on authenticated webhooks
The problem with HTTPBasicAuthHandler is that it will first attempt to make an

unauthenticated request, and will retry with authentication only if a 401

response was seen. However, some servers respond with 403 if the right

credentials are not supplied right away.

This is a forward-ported version of my patches on top of 3.0.18, which is powering our production site.
Note: It is best to review the changes one commit at a time. The patch series is available publicly on Github.