run tests normally if Build.pm is not a Tester

If the Build.pm is not Panda::Tester the tests will be run as normal.
Currently if a Build.pm file exists but does not supply a test method
no tests are being run. This means many Nativecall reliant modules are
not being tested in the smoketests etc.
Merge pull request #102 from carbin/panda-test

run tests normally if Build.pm is not a Tester

Looks solid, and it's easier for me to test once merged.  ;)