If you run "/Applications/Second Life Beta Materials.app", and the version
manager directs you to update to a .dmg containing a release candidate whose
app bundle name is "Second Life Viewer.app", update_install.py used to copy
the contents of "Second Life Viewer.app" into "/Applications/Second Life Beta
Materials.app". Changed it so that if the application bundle name differs, we
leave the running app bundle alone, installing instead to the app bundle name
from the .dmg.

Remove the offending code.

instead of errno.EEXIST. Sigh.

Remove mac-updater subtree from viewer source, along with the
update_install bash script that invoked it. Remove all mention of mac-updater
in CMakeLists.txt files and in viewer_manifest.py.
Change Mac update_install bash script references in viewer_manifest.py and in
llupdaterservice.cpp (which invokes it) to new Python update_install.py.
Add update_install.py, messageframe.py (which puts up some Tkinter UI) and
janitor.py (cloned from vita, it's exactly what we need here).