OpenSystemsDevelopment / qpdf

Use autoconf rather than ifdefs to determine what format string to use
for long long.

Fixes qpdf/qpdf#417

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

This was added in C++11.

Thanks to Zdenek Dohnal <zdohnal@redhat.com> for contributing the code
used for the gnutls crypto provider.

Just rename MD5 -> MD5_native in place so that git annotate will show
the lines as having originated there.

Includes updates to m4/ax_cxx_compile_stdcxx.m4 to make it work with
msvc, which supports C++-11 with no flags but doesn't set __cplusplus
to a recent value.

Use PointerHolder in several places where manually memory allocation
and deallocation were being used. This helps to protect against memory
leaks when exceptions are thrown in surprising places.

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.

Change from unsigned long to int since we pass enumerated type values
to this field.

Based on sizeof(size_t). Assumes 64 if not 32.

If set, we avoid using Windows I/O HANDLE, which is disallowed in some
versions of the Windows SDK, such as for Windows phones.
QUtil::same_file will always return false in this case. Only applies
to Windows builds.

The original QPDF is only required now when the source
QPDFObjectHandle is a stream that gets its stream data from a
QPDFObjectHandle::StreamDataProvider.

Give objects descriptions and context so it is possible to issue
warnings instead of fatal errors for attempts to access objects of the
wrong type.