Allows N instances of tests run in parallel, each running 1/N parts
of the test suite under Valgrind, to speed things up.
* tr/test-v-and-v-subtest-only:
perf-lib: fix start/stop of perf tests
test-lib: support running tests under valgrind in parallel
test-lib: allow prefixing a custom string before "ok N" etc.
test-lib: valgrind for only tests matching a pattern
test-lib: verbose mode for only tests matching a pattern
test-lib: self-test that --verbose works
test-lib: rearrange start/end of test_expect_* and test_skip
test-lib: refactor $GIT_SKIP_TESTS matching
test-lib: enable MALLOC_* for the actual tests
04f2ddda84