Allow CommonJS modules to be an empty string.
Allow CommonJS modules to be an empty string.

We were making a typical JavaScript mistake testing a module for
truthiness instead of checking that it was undefined.

Fixes COUCHDB-1223
Backport of r1176677 from trunk



git-svn-id: eed9d206131b186e33f41325873c3684e4065c95@1176679 13f79535-47bb-0310-9956-ffa450edef68

cloudant/bigcouch,andrejb/cloudant_bigcouch,andrejb/cloudant_bigcouch,cloudant/bigcouch,cloudant/bigcouch,Asquera/bigcouch,georgemarshall/bigcouch,PerilousApricot/bigcouch,linearregression/bigcouch,Asquera/bigcouch,PerilousApricot/bigcouch,linearregression/bigcouch,kofron/bigcouch,georgemarshall/bigcouch,breezjw/bigcouch,linearregression/bigcouch,andrejb/cloudant_bigcouch,linearregression/bigcouch,breezjw/bigcouch,linearregression/bigcouch,cloudant/bigcouch,Asquera/bigcouch,Asquera/bigcouch,cloudant/bigcouch,andrejb/cloudant_bigcouch,breezjw/bigcouch,breezjw/bigcouch,kofron/bigcouch,georgemarshall/bigcouch,georgemarshall/bigcouch,breezjw/bigcouch,PerilousApricot/bigcouch,PerilousApricot/bigcouch,breezjw/bigcouch,andrejb/cloudant_bigcouch,kofron/bigcouch,cloudant/bigcouch,Asquera/bigcouch,kofron/bigcouch,linearregression/bigcouch,kofron/bigcouch,georgemarshall/bigcouch,cloudant/bigcouch,georgemarshall/bigcouch,PerilousApricot/bigcouch,kofron/bigcouch,Asquera/bigcouch,PerilousApricot/bigcouch,linearregression/bigcouch,andrejb/cloudant_bigcouch,andrejb/cloudant_bigcouch