(Bug 5219) Make sure the DW cgi-bin is in @INC

In my testing, this fixes the issue Dre pointed out where the test
would fail if the DW cgi-bin was not already in @INC (e.g. by
setting PERL5LIB in the shell, which is what I had done).
Merge pull request #526 from kareila/bug5219-compiletest

(Bug 5219) Make sure the DW cgi-bin is in @INC