try/catch the import call so that in event of an exception
(e.g. assertions are turned on), we'll still release the
importer -- thus unmapping the rom, and generally making
life happier.
Ensure classData isn't null before blindly trying to access
it's ->name
Preliminary support for 2.0 images.  These introduce a few new
data types: 0xc0, 0xc1, 0xc3.  Thankfully they mirror to the
existing values, 0x40, 0x41, 0x43.

For sanity checking purposes, ensure we're always dealing
with 0, 1 or 3.  If not, error out.  And that if we're
dealing with c, that the ROM major is 2.0.

The 2.0 images seem to introduce two unusual values in
frame class slots. 0x32 and 0x132.  These seem to map to
CodeBlock and CFunction.  So we'll do some swapping if
we aren't able to get back a class for the frame, and
we're in a 2.0 image.

To be useful for 2.0 images, we'll need to start reading in
the "high image" as well.