OpenSystemsDevelopment / qpdf

This makes the code simpler than having to create a buffer of a fixed
size and copy the string to it.

This rework makes xref reconstruction run much faster and use much
less memory.

With QPDF allowing integers to contain 64-bit quantities, this change
is necessary to be able to linearize files whose sizes might be larger
than 10 digits.

This makes it possible to store offsets that are larger than 2 GB in
the trailer dictionary.

Provide option to show test output if requested.

This just makes it safer to pull up this file in an editor.

Also updated pdf_from_scratch test driver to use the new factories,
and made some cosmetic improvements and documentation updates for the
emptyPDF() method.

Place user-specified CPPFLAGS and LDFLAGS later so that user-specified
non-standard paths that have old versions of qpdf don't cause the
build to fail.

off_t is used internally only when needed to talk to standard
libraries.  This requires that the "long long" type be supported by
the compiler.

Update the build to support new external-libs layout, and autoconf
options to specify windows word size.  Split make_windows_releases
into multiple scripts.

Thanks Tobias Hoffmann for noticing the error.