Merge changes I32e726c7,I1dc9a708,I09cc335b,Ifb8a66ab,I0e2c25bc, ...

* changes:
  versioner: whitelist atexit, turn on symbol checking by default.
  versioner: add missing test.
  versioner: fix false positive with functions only available as inlines.
  versioner: improve error output slightly.
  versioner: merge stdout and stderr in the test runner.
  versioner: clean up tests, test runner.
  versioner: ignore functions that are __INTRODUCED_IN_FUTURE.
  versioner: autodetect paths when no specified.
  versioner: improve usage messages.
  Remove __cachectl.