Revamp internal _get_entry.
Revamp internal _get_entry.

It should deal in exacts; we emulate some bad behavior
of previous APIs out at the API edge.

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

clalancette/pyiso,clalancette/pycdlib