Modified the "pdfparanoia" script in bin/ so it uses Argparse and the "with" context statement.

As python 2.6 was already commented as a potential environment, there seemed little
reason to not use Argparse rather than a sys.argv popping system; argparse offers
automatically generated usage documentation and can offer useful errors when input
is incorrect.

The "with" context statement is also highly excellent and should be used wherever
legacy support for old-timers using 2.6 is not needed.
Fixed a few bugs so reading from stdin now works. Involves a potentially costly recast of file contents as StringIO.