OpenSystemsDevelopment / qpdf

Manual edits for cases not handled by search and replace

Using search and replace.

If /AP is a dictionary of streams rather than a dictionary of
dictionaries, disregard /AS, which is supposed to point to a subkey of
one of the dictionaries. This fix prevents qpdf's annotation
flattening from discarding some annotations when /AS is erroneously
set.

Add new method QPDF::newReserved()

Add new convenience class QPDFObjGen::Guard

#863 uses a single null object for nulls that were previously implicit. In
certain circumstances this shared null object gets destroyed (i.e changed
to a QPDF_Destroyed object) when a QPDF object is destroyed.

Modify the QPDF destructor so that null objects get disconnected from the
dying QPDF object but not destroyed to prevent this from happening.

'#' was omitted from the list of chars that need to be escaped.

Also, move _qpdf_data and to new header filer _qpdf_error to new header
file qpdf-c_impl.hh