OpenSystemsDevelopment / qpdf

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.

Most Linux distributions include qpdf now, so there is no need to
distribute our own spec file.

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.

The latest automated mingw-w64 build's libstdc++-6.dll crashes with
qpdf 4.1.0, but libstdc++-6.dll can be replaced with one from a newer
build.

When copying dlls, make sure to only consider DLLs whose type matches
the type of what is loading them.

Windows fix: QPDFObject::ParserCallbacks::terminateParsing() was not
declared with QPDF_DLL.

Explicitly state how QPDF handles empty passwords when writing files.
Apparently some libraries treat the empty string as the owner password
as an instruction to generate a random password.

Prepare update for TODO for publication since there is useful
information there for people looking at the repository.

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.

Enable C4996, deprecation/security warnings, which helps for Windows 8
certification.  Stop enabling C4267, which was warning about
conversions between size_t and other integer types.

Also separate C and C++ warning flags.

Make --enable-werror work properly on msvc, handle extra warnings
flags for msvc in configure.ac instead of hardcoding into
make/msvc.mk, separate warnings flags into WFLAGS in autoconf.mk to
avoid duplication and to make it easier to override.

Add QUtil::hex_encode to encode binary data has a hexadecimal string,
and use it in place of sprintf where possible.

Change iteration to use size_t instead of int.  The code should be
equivalent in all reasonable cases, but the original way this was
coded was causing a test failure with gcc 4.8.0 on ppc64.  See
https://bugzilla.redhat.com/show_bug.cgi?id=915321 for additional
information.