[boost] libs/regex/build/Jamfile.v2 missing "import testing"

In a partial installation (not all submodules installed), running b2 in the Boost root says: libs\regex\build\Jamfile.v2:93: in modules.load ERROR: rule "unit-test" unknown in module "Jamfile". because libs/regex/build/Jamfile.v2 uses the unit-test rule, defined in testing.jam, but does not have "import testing ;". Adding that line fixes it. I've no idea why it works in a full installation - probably because someone else imports testing first before it gets to regex.