tor-0.2.5.5-alpha and git/HEAD fail to build tests when --enable-bufferevents
Currently tor fails to build its test when enabled with bufferevents because an #ifndef USE_BUFFEREVENTS hides bucket_millis_empty() and friends. This is fine if we don't run tests, but if we do, we need these functions in src/or/libtor-testing.a when linking src/test/test.
This patch moves the functions outside the #ifndef and exposes them.
See downstream bug:
https://bugs.gentoo.org/show_bug.cgi?id=510124