Bug 695112: only patch height values in JPEG streams

If the reported height is 0 or too large, use the image size reported
in the PDF itself instead (in the case of height 0, the JPEG library
is supposed to read the correct value from the DNL segment, but libjpeg
doesn't support that).
Correctly round PNG image resolution

Currently, png_read_phys always rounds the resolution down. Many images
have a resolution just slightly shy of 96 DPI and are thus rendered too
large when they're resized from 95 to match the required 96 for output.
minor clean-up
truncate the xref after compacting

pdf_write_document still writes the entire xref with references to all
freed objects even if the xref has been compacted which makes the
result of mutool clean -ggg larger than necessary.
Remove platform/debian directory.

These files are maintained by debian. Now that debian updates the mupdf package
more regularly there is no need for us to keep our own debian packaging files.

https://packages.debian.org/unstable/main/mupdf