skip aggregation tests on MongoDB < 2.2. PERL-215
Drop all created collections in dbref.t
Merge pull request #71 from ilmari/dbref-t-cleanup

Drop all created collections in dbref.t
factor out test boilerplate to a module
rm test boilerplate
factor out test boilerplate to a module
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate
rm test boilerplate