OpenSystemsDevelopment / qpdf

A new private overload of QPDF::makeIndirectObject breaks pikepdf's
build, so renaming function.

…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.

* 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.

Base implementation of the buffer on std::basic_string<unsigned char>.

This reverts commit 416d9668ee97c54a692d9280364746ce8aeeed43.

This commit causes numerous failures in the pikepdf test suite and
also causes a symbol to disappear from the public API. More
investigation will be required.

Removing an element from a set with iterator is constant time, and
std::set specifies that other operations on the set do not invalidate
existing iterators.

Some new symbols were exported.

These markers are being added for nested classes that are already
marked with QPDF_DLL_CLASS. They don't make any different on Linux,
but they matter on Windows.