Since we're parsing segment headers for random-access jbig2 inputs
already, just always do that and get the image dimensions from the
PageInformation segment data. Not all that much more code, and it
makes this script much more pleasant to use.
jbig2 data in PDFs is in the embedded organization, which is like the
sequential organization with the file header removed.
That means jbig2 files using the random-access organization need to
be transformed to be supported. A random-access jbig2 has all segment
headers at the start, followed by the data of all segments. Decode
all headers and rewrite them to the sequential organization, where
each segment header is followed by that segment's data.
The motivation is that almost all of the jbig2 files in
ghostpdl/test/jbig2 use the random-access organization.
Most image viewers can't display JBIG2 files.
All PDF viewers can display JBIG2 files.
This is useful for checking that PDF viewers render JBIG2 files the
same way we do.
