OpenSystemsDevelopment / qpdf

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

This includes QPDF::copyForeignObject and supporting foreign objects
as arguments to addPage*.

Previous versions of qpdf incorrectly passed arbitrary objects from
/Pages objects down to individual pages in direct contradition with
the PDF specification.  These are now left in /Pages.  When
intermediate /Pages nodes are being discarded as when the /Pages tree
is being flattened, a warning is issued when unknown keys are
encountered.

Refactored optimizePagesTree to pushInheritedAttributesToPage and made
public