tests/test-fuzz-targets.t

py3: use pycompat.strkwargs() to convert kwargs' key to str

Differential Revision: https://phab.mercurial-scm.org/D2043

#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