codeintel: don't use nsSupportsPrimitiveCString off the main thread

enumerating categories and looking up contract ids use nsISupportsCString
it's yet another one of those components that hate not being on the main thread
so proxy the whole chunk (synchronously) to the main thread; we don't need
to do that on a background thread.

(integrated from komodo (trunk) change 81775 by marky)

git-svn-id: http://svn.openkomodo.com/repos/openkomodo/trunk@13589 b87d16e7-d29f-4ee1-b5ec-817d645d335f