Fix undefined sub name, clash with Test::Builder::Level

This pull request fixes the following erroneous output that occurs with more recent versions of Test::Builder, and allows Test::Pretty to work correctly:

> # $Test::Builder::Level is invalid. Testing library you are using is broken. : 4 at /Users/ali/perl5/perlbrew/perls/perl-5.14.2/lib/site_perl/5.14.2/Test/Warnings.pm line 134.
> #       Test::Warnings::had_no_warnings("no (unexpected) warnings (via done_testing)") called at /Users/ali/perl5/perlbrew/perls/perl-5.14.2/lib/site_perl/5.14.2/Test/Warnings.pm line 101
> #       Test::Warnings::__ANON__(Test::Builder=HASH(0x7fd284000f90)) called at /Users/ali/perl5/perlbrew/perls/perl-5.14.2/lib/site_perl/5.14.2/Test/More.pm line 220
> #       Test::More::done_testing() called at t/14-cron-jobs/10-search-indexer.t line 46
> # Use of uninitialized value $sub in pattern match (m//) at /Users/ali/perl5/perlbrew/perls/perl-5.14.2/lib/site_perl/5.14.2/Test/Pretty.pm line 275.

I tested the 0.31 tarball locally and everything works fine, and it passes all existing tests in the suite.