ENH: lazier handling of dynamic libraries
- previously always called dlclose on opened libraries when destroying the dlLibraryTable. However, by force closing the libraries the situation can arise that the library is missing its own code that it needs on unload (#1524). This is also sometimes evident when closing VTK libraries for runTimePostProcessing (#354, #1585). - The new default is to not forcibly dlclose any libraries, unless the dlcloseOnTerminate OptimisationSwitch specifies otherwise. - The dlLibraryTable::close() method can be used to explicitly close all libraries and clear the list. - The dlLibraryTable::clear() method now only clears the entries, without a dlclose.