FStream: Expose is_open
These are minor changes to allow VTK to replace std::ifstream/ofstream with vtksys::ifstream/ofstream where the file names are properly handled for unicode in Windows
The change exposes is_open() in ifstream/ofstream.
Some redundant code is also removed where KWSYS already handles ToWindowsExtendedPath() in the ifstream/ofstream constructor
Topic-rename: FStream-is_open
Edited by Brad King