For full completion functionality - where swcs are included when searching for the completions results - you need to have the 'nokogiri' and 'rubyzip' gems installed. The default ruby shipping on OS X is 1.8.7 so the easiest solution is to switch to the system default ruby and install the nokogiri and rubyzip gems there.
However the following should also work....
TextMate 2, rvm (with ruby 1.9.3 installed) and the AS3 bundle are installed on your machine and when you try to autocomplete an error gets thrown.