On upgrade from 10.04 to 10.10 BETA I experienced the same, (I should have researched before jumping in to BETA)..
sudo dpkg-divert --remove /usr/lib32/libGL.so.1.2
Notice the /lib32 not /lib as I am running on a 64bit platform.
This seems to allow a purge to work but leaves some stale directories.
On upgrade from 10.04 to 10.10 BETA I experienced the same, (I should have researched before jumping in to BETA)..
sudo dpkg-divert --remove /usr/lib32/ libGL.so. 1.2
Notice the /lib32 not /lib as I am running on a 64bit platform.
This seems to allow a purge to work but leaves some stale directories.