broken 12.04 upgrade now gives g_mutex_trylock error

[Charlie Zender]

During the over-the-net upgrade from oneiric to precise
(11.10->12.04), the upgrade procedure broke.
Now when trying to restart it with update-manager -d,
an error occurs. The same error occurs when trying
to start many important programs like firefox, thunderbird:

zender at neige:~$ update-manager -d
ERROR:root:Could not find any typelib for Unity
WARNING:root:can not import unity GI cannot import name Unity
/usr/bin/python: symbol lookup error:
/usr/lib/x86_64-linux-gnu/libpangoft2-1.0.so.0: undefined symbol:
g_mutex_trylock

How can I fix this error?
Or back completely out of the upgrade to start over?

Thanks,
c
-- 
Charlie Zender, Department of Earth System Science
University of California, Irvine 949-891-2429  )'(