properly implement pkgRecord::Parser for *.deb files

properly implement pkgRecord::Parser for *.deb files

Implementing FileName() works for most cases for us, but other
frontends might need more and even for us its not very stable as
the normal Jump() implementation is pretty bad on a deb file and
produce errors on its own at times.
So, replacing this makeshift with a complete implementation by
mostly just shuffling code around.