CHOP-955, CHOP-957: Prioritize indra.util.llmanifest in same source repo.

It seems that certain build hosts have an (obsolete? broken?) install of
indra.util.llmanifest under the system Python. If we append the local repo
indra/lib/python to sys.path, viewer_manifest.py pulls in the broken
llmanifest. Prepend to sys.path instead to ensure we get the right one.