OpenSystemsDevelopment / qpdf

* Handle error conditions that occur when using the object handle
  interfaces. In the past, some exceptions were not correctly
  converted to errors or warnings.
* Add more detailed information to qpdf-c.h
* Make it possible to work more explicitly with uninitialized objects

Return new qpdf_oh from qpdf_oh_wrap_in_array when input is already an array.
Update some doc comments in qpdf-c.h.

When adding a QPDFObjectHandle to an array or dictionary, if possible,
check if the new object belongs to the same QPDF. This makes it much
easier to find incorrect code than waiting for the situation to be
detected when the file is written.

This was originally not public because I wanted to get rid fo the
pages cache, but I recently realized there were deep reasons not to do
that, and the author of pikepdf wanted this, so I decided to make it
public.

Also improve behavior around direct vs. indirect resources.

If not found in the field hierarchy, /Q and /DA are supposed to be
looked up in the document-level form dictionary. /DR is supposed to
only come from the document dictionary.

This results in a performance penalty of 1% to 2% when replaceObject
and swapObjects are never called and a somewhat larger penalty if they
are called, but it's worth it to avoid very confusing behavior as
discussed in depth in qpdf#507.