OpenSystemsDevelopment / qpdf

Even though this is disallowed by the spec, files like this have been
encountered in the wild.

Various PDF digital signing tools do not encrypt /Contents value in
signature dictionary. Adobe Acrobat Reader DC can handle a PDF with
the /Contents value not encrypted.

Write Contents in signature dictionary without encryption

Tests ensure that string /Contents are not handled specially when not
found in sig dicts.

It seems better not to compress signature dictionaries. Various PDF
digital signing tools, including Adobe Acrobat Reader DC, do not
compress signature dictionaries.

Table 8.93 "Entries in a signature dictionary" in PDF 1.5 reference
describes that /ByteRange in the signature dictionary shall be used to
describe a digest that does not include the signature value
(/Contents) itself.

The byte ranges cannot be determined if the dictionary is compressed.

Table 8.93 "Entries in a signature dictionary" in PDF 1.5 reference
describes that the value of Contents entry is a hexadecimal string
representation when ByteRange is specified.

This commit makes QPDF always uses hexadecimal strings representation
instead of literal strings for it.

It's detected in QPDFWriter instead of at parse time because I can't
figure out how to construct a test case in a reasonable time. This
commit moves the fuzz file into the regular test suite for a QTC
coverage case.

Just because we know an indirect reference is null, doesn't mean we
shouldn't keep it indirect.

For some reason, qpdf from the beginning was replacing indirect
references to null with literal null in arrays even after removing the
old behavior of flattening scalar references. This seems like a bad
idea.

This message used to only appear for PDF >= 1.2. The invalid name is
valid for PDF 1.0 and 1.1. However, since QPDFWriter may write a newer
version, it's better to detect and warn in all cases. Therefore make
the warning more informative.

This also reverts the addition of a new checkLinearization that
distinguishes errors from warnings. There's no practical distinction
between what was considered an error and what was considered a
warning.

* Several assertions in linearization were not always true; change
  them to run time errors
* Handle a few cases of uninitialized objects
* Handle pages with no contents when doing form operations
* Handle invalid page tree nodes when traversing pages

Bounding box X coordinates could be truncated, causing them to be off
by a fraction of a point. This was most likely not visible, but it was
still wrong.

Temporarily skip fuzz tests on Windows. There are Windows-specific
failures to address later.

On read, ignore /DecodeParms when empty list; on write, delete it.
Some files have been found that include an empty list for
/DecodeParms, but this is not technically compliant with the spec, and
the only sensible interpretation is to treat it as if there are no
decode parameters.

Remove dependency on the behavior of perl for reliable creation of
Unicode file names on Windows.