revert removal of fstream.hpp header in fs.h

This is required for some architectures.

Author: kallewoof

src/fs.h

@@ -12,6 +12,7 @@
 #endif
 
 #include <boost/filesystem.hpp>
+#include <boost/filesystem/fstream.hpp>
 
 /** Filesystem operations and types */
 namespace fs = boost::filesystem;