Fix a bug in pycdlib-genisoimage with duplicate names.
Fix a bug in pycdlib-genisoimage with duplicate names.

The problem would happen when you had two mangled files
that had different starting mangled names, but reduced
down to the same mangled prefix.  Fix this by checking
the prefixes before assigning a name.

Signed-off-by: Chris Lalancette <281cd07d7578d97c83271fbbf2faddb83ab3791c@gmail.com>

clalancette/pycdlib,clalancette/pyiso