Using this option (only available in debug builds) makes curl always
call curl_easy_duphandle() on the handle before using it.
To help us catch curl_easy_duphandle() mistakes better.
Add a CI job using this.
Bonus: the previous runtests option -e is now also supported as
--test-event
Closes#15504
missing CRs and modified %hostip
lib556/test556: use a real HTTP version to make test reuse more convenient
make sure the weekday in Date headers matches the date
test61: replace stray "^M" (5e 4d) at the end of a cookie with a '^M' (0d)
Gets the test working with external proxies like Privoxy again.
Closes#6463
