OpenSystemsDevelopment / qpdf

Also accept -accessibility=n with 256 bit keys even though it will be
ignored.

For std::string and std::vector, replace operator[] with at.  This was
done using an automated process.  See README.hardening for details.

If not available, give an error.  The user may also configure qpdf to
use an insecure random number generator.

Ideally, the library should never call assert outside of test code,
but it does in several places.  For some cases where the assertion
might conceivably fail because of a problem with the input data,
replace assertions with exceptions so that they can be trapped by the
calling application.  This commit surely misses some cases and
replaced some cases unnecessarily, but it should still be an
improvement.

In places where std::vector<T>(size_t) was used, either validate that
the size parameter is sane or refactor code to avoid the need to
pre-allocate the vector.

The /W array was not sanitized, possibly causing an integer overflow
in a multiplication. An analysis of the code suggests that there were
no possible exploits based on this since the problems were in checking
expected values but bounds checks were performed on actual values.

The faulty code was only used during explicit checks of linearization
data.  Those checks are not part of normal reading or writing of PDF
files.

Better sanity check inputs to bit stream reader

4.2.0 was binary incompatible in spite of there being no deletions or
changes to any public methods.  As such, we have to bump the ABI and
are fixing some API breakage while we're at it.

Previous 4.3.0 target is now 5.1.0.

Thanks to Jiri Popelka from Red Hat for sending the output of a
Coverity run over qpdf.

Space rather than newline after xref, missing /ID in trailer for
encrypted file.  This enables qpdf to handle some files that xpdf can
handle.  Adobe reader can't necessarily handle them.

Even though this case is not valid according to the spec, it has been
seen, and caused an internal error.

Rework QPDFWriter to always track old object IDs and QPDFObjGen
instead of int, thus not discarding the generation number.  Switch to
QPDF::getCompressibleObjGen() to properly handle the case of an old
object eligible for compression that has a generation of other than
zero.

In internal code and examples, replace calls to getObjectID() and
getGeneration() with calls to getObjGen() where possible.

This is safer than getObjectID() and getGeneration() for many uses.

Versions prior to 4.6 didn't allow gcc diagnostic pragmas with push
and pop and to appear anywhere in the file.  Just let the warning be
there for those versions.

Remove const qualifier from getTypeCode and get getTypeName methods of
QPDFObjectHandle, make them work properly for indirect objects, and
exercise them much better in the test suite.

Make remaining calls to fopen and strerror use strerror_s and fopen_s
on MSVC.

fopen was previuosly called wrapped by QUtil::fopen_wrapper, but
QUtil::safe_fopen does this itself, which is less cumbersome.

Remove needless calls to open, close, and fileno; call remove instead
of unlink.

Put a specific comment marker next to every piece of code that MSVC
gives warning 4996 for.  This warning is generated for calls to
functions that Microsoft considers insecure or deprecated.  This
change is in preparation for fixing all these cases even though none
of them are actually incorrect or insecure as used in qpdf.  The
comment marker makes them easier to find so they can be fixed in
subsequent commits.

Make them safer by avoiding any internal limits and replacing sprintf
with std::ostringstream.