OpenSystemsDevelopment / qpdf

Issue #399 mentioned a use case for which qpdf has support, but the
fact that it is supported was not documented or in the test suite,
making it vulerable to accidental breakage.

StreamDataProvider::provideStreamData now has a rich enough API for it
to effectively proxy to pipeStreamData.

If a page contains a form XObject, also filter the form XObject and
remove its unreferenced resources.

fix-qdf assumes there is exactly one XRef stream and that it is at the
end of the file.

If the value of /CS in the inline image dictionary was is key in the
page's /Resource -> /ColorSpace dictionary, properly resolve it by
referencing the proper colorspace, and not just the name, in the
external image dictionary.

This change makes it possible to get both the user and owner password
from the file name of all the encryption test files.

Allow exit status-based checking of whether a file is encrypted or
requires a password without necessarily supplying the correct
password. Useful for scripting.

For wildcard expansion to work properly with the msvc binary, it is
necessary to link with setargv.obj or wsetargv.obj, depending on
whether wmain is in use.

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.