Ensure prod build assertions are only made once.

When running `expectAssertion(callbackFN)` `this.expecteds` was an empty
array (because the assertion was already done) so it passed the previous
guard.

Now we just check to see if `this.expecteds` AND `this.actuals` are
empty before short curcuiting.
Merge pull request #145 from rwjblue/ensure-prod-deprecations-happen-only-once

Ensure prod build assertions are only made once.