* Define it even though previous experiments have shown it to be
unnecessary since it seems like it may be necessary after all
* Add QPDF_DLL_CLASS to QPDFObjectHelper and QPDFDocumentHelper in
case there's some future unknown reason why someone may want to have
them and/or in case it helps with the weird
QPDFNameTreeObjectHelper problem.
An indirect object reference to 0, 0 is invalid. If it appears in the
file or is parsed from a string, the parser catches it. This check
would only be useful for someone explicitly calling getObject with 0,
0, and that would trigger an error during resolve().
Replace operator== and operator!=, which were testing for the same
underlying object, with isSameObjectAs. This change was motivated by
the fact that pikepdf internally had its own operator== method for
QPDFObjectHandle that did structural comparison. I backed out qpdf's
operator== as a courtesy to pikepdf (in my own testing) but also
because I think people might naturally assume that operator== does a
structural comparison, and isSameObjectAs is clearer in its intent.
QPDFValueProxy wasn't a good name for it. We decided the evil of
having the header file be named QPDFObject_private.hh was less than
the evil of having the class be named something other than what it
should have been named.
I decided that it's actually fine to copy a direct object to another
QPDF. Even if we eventually prevent a QPDFObject from having multiple
parents, this could happen if an object is moved.
When a QPDF is destroyed, changing indirect objects to direct nulls
makes them effectively disappear silently when they sneak into other
places. Instead, we should treat this as an error. Adding a destroyed
object type makes this possible.
The qpdf member was already sufficient. Removing this actually fixed a
few pre-existing issues around detecting foreign ownership and
allowing certain conditions to be warnings rather than exceptions.
