OpenSystemsDevelopment / qpdf

Add new convenience class QPDFObjGen::Guard

Also, name the type QPDFValue::Description.

Avoid dynamic casting.

Exclude uninitialized, destroyed and reserved objects.

…ternal2 and copyObject2

copyObject2 repeats a second time what
new_obj = QPDFObjectHandle(obj->copy(true))
in shallowCopyInternal2 already did.

…ternal2 and copyObject2

Have separate versions for unsafeShallowCopy, shallowCopy and makeDirect.

Add optional parameter shallow. Change logic errors to runtime errors.

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.