Fix bug #410274 - sys.prefix isn't always set.
Fix bug #410274 - sys.prefix isn't always set.

If after calculating sys.path we do not have sys.prefix set, we loop over all path entries checking if one can point to our home directory.

sk-/python2.7-type-annotator,sk-/python2.7-type-annotator,sk-/python2.7-type-annotator