wireprotoserver: define and use parse_qs from urllib
The cgi module is deprecated since Python 2.6. Let's replace uses
of it in wireprotoserver with a similar function from urllib.
Differential Revision: https://phab.mercurial-scm.org/D2094
#require clang-libfuzzer test-repo
$ cd $TESTDIR/../contrib/fuzz
$ make
Just run the fuzzer for five seconds to verify it works at all.
$ ./bdiff -max_total_time 5