Fix api jars-by-groupname performance
Fix api jars-by-groupname performance

Sqlite explain shows that without restricting join queries by
group_name, sqlite is doing full table scans.
Quick dotimes 1000 shows improvement from 15 seconds to 800ms on my
computer.

xeqi/clojars-web,clojars/clojars-web,codonnell/clojars-web,dotemacs/clojars-web,leonid-shevtsov/clojars-web,technomancy/clojars-web,clojars/clojars-web,xeqi/clojars-web,beppu/clojars-web,nberger/clojars-web,thiagofm/clojars-web,clojars/clojars-web,tobias/clojars-web,ato/clojars-web,codonnell/clojars-web,nberger/clojars-web,tobias/clojars-web,tobias/clojars-web,dotemacs/clojars-web,technomancy/clojars-web,ato/clojars-web