OpenSystemsDevelopment / qpdf

This makes all integer type conversions that have potential data loss
explicit with calls that do range checks and raise an exception. After
this commit, qpdf builds with no warnings when -Wsign-conversion
-Wconversion is used with gcc or clang or when -W3 -Wd4800 is used
with MSVC. This significantly reduces the likelihood of potential
crashes from bogus integer values.

There are some parts of the code that take int when they should take
size_t or an offset. Such places would make qpdf not support files
with more than 2^31 of something that usually wouldn't be so large. In
the event that such a file shows up and is valid, at least qpdf would
raise an error in the right spot so the issue could be legitimately
addressed rather than failing in some weird way because of a silent
overflow condition.

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.

Setting encryption permissions for R >= 3 set permission bits in
groups corresponding to menu options in Acrobat 5. The new API allows
the bits to be set individually.

On certain operations, such as iterating through all objects and
adding new indirect objects, walk through the entire object structure
and explicitly resolve any indirect references to non-existent
objects. That prevents new objects from springing into existence and
causing the previously dangling references to point to them.

There were a few places in the code that were checking that a pointer
wasn't null before deleting it, even though C++ has always allowed
delete 0. Most of the code did not perform these checks.

Turns out you can keep adding zero to a number over and over again and
it just doesn't get any bigger. Who would have known?

Implement a TokenFilter class and refactor Pl_QPDFTokenizer to use a
TokenFilter class called ContentNormalizer. Pl_QPDFTokenizer is now a
general filter that passes data through a TokenFilter.

This is useful only for debugging the linearization code.

Tweak the message so that we inform the user that we are mitigating
data loss.

The latter catches underflow/overflow.

Reduce code duplication

Remove duplicated coverage cases from Sahil's code so existing test
suite passes.

* Add support for PCLm using setPCLm() and writePCLm() methods in
  QPDFWriter.hh and QPDFWriter.cc
* Add a function writePCLmHeader() for PCLm header in QPDFWriter

There is no need for a --precheck-streams option. We can do the
precheck without imposing any penalty, only re-encoding the stream if
it fails the first time.

This commit adds several API methods that enable control over which
types of filters QPDF will attempt to decode. It also adds support for
/RunLengthDecode and /DCTDecode filters for both encoding and
decoding.

Add a newline unconditionally before endstream even if a newline was
already written as part of the stream data.

Bad /W in an xref stream could cause a division by zero error. Now
this is handled as a special case.

When requested, QPDFWriter will do more aggress prechecking of streams
to make sure it can actually succeed in decoding them before
attempting to do so. This will allow preservation of raw data even
when the raw data is corrupted relative to the specified filters.

Since we have to bump soname, remove some private methods that were
just there for binary compatibility

For non-encrypted files, determinstic ID generation uses file contents
instead of timestamp and file name. At a small runtime cost, this
enables generation of the same /ID if the same inputs are converted in
the same way multiple times.

QPDFWriter was trying to make /Filter and /DecodeParms direct in all
cases, but there are some cases where /DecodeParms may refer to a
stream, which can't be direct. QPDFWriter doesn't actually need
/DecodeParms to be direct in that case because it won't be able to
filter the stream. Until we can handle this type of stream, just don't
make /Filter and /DecodeParms direct if we can't filter the stream
anyway.

Fixes #34

Fix problem: if the last object in the first part of a linearized file
had an offset that was below 65536 by less than the size of the hint
stream, the xref stream was invalid and the resulting file is not
usable.

Also remove some trivial, non-functional code.