travis try jruby 1.7.16
unset rvm_debug on travis to avoid rvm specific issue rvm#3069
guarded tarpit spec require
Revert "travis try jruby 1.7.16"

http://rubies.travis-ci.org/ suggests Travis should have 1.7.18/

This reverts commit 483ba55cb57e3363ffba005a89acb69df166263b.