Fix the /send_join and /send_leave endpoints, so that they use the v2 endpoints as mandated by MSC1802. Also comment out the SyTest tests that are failing because of lack of support for the v1 endpoints.
We were escaping the URL before performing any pattern matching on it.
This meant that if you sent data that URLdecoded to a "/", it would count as
a "/" in the URL, potentially causing a 404. This was causing some flaky tests
with some randomly-generated query parameters.
Now, we keep URLs encoded while doing the pattern matching, and only afterwards
do we URL decode each query parameter individually before passing them to their
respective handler functions.
github.com/gorilla/mux was also updated to v1.7.3 to fix a bug with URL encoding and subrouters.
