Leave ENV['GEM_PATH'] alone if it is nil
Merge pull request #161 from robababa/issue-161

Remove GEM_PATH line 93 from runspecs?
Prevent circularity in Column#as_json.  

(Latest failure only arose for jruby / rails 3.2 / postgresql, but the fix should be harmless for other combos)
Merge branch 'master' of github.com:lomba/schema_plus