httprepo: use separate handlers for HTTP and HTTPS
This is needed to keep the code in keepalive.py from sharing
the same connection between HTTP and HTTPS.
52ce0d6bc375 explains why we were using a single handler.
This should fix issue892.
# should print nothing
# should fail
abort: path 'b/x' is inside repo 'b'
abort: path 'b/x' is inside repo 'b'
# should fail
abort: path 'b/x' is inside repo 'b'
# should arguably print nothing
# should fail
abort: path 'b/a' is inside repo 'b'