pdf-merge.py: Update dump parser for pdftk v1.45

pdf-merge.py: Update dump parser for pdftk v1.45

On Tue, Jan 29, 2013 at 08:15:57AM -0800, Tsung-Han Yang wrote:
> I've attached the dumpdata message. I've just installed pdftk on
> windows yesterday. I've attached the diff file with -u, too.
> ...
> It looks like my pdf has some metadata like "InfoBegin" without ":"
> in the line.

The new lines in the dump are due to the addition of m_begin_mark in
pdftk between v1.44.1 and v1.45:

Sid Stewart wrote:
> Added record delimiters to dump_data output to help make parsing
> more reliable.