srogue: add and use md_fdopen(). The implementation was copied from rogue4. Using fdopen() is necessary because the scorefile needs both encread() and encwrite(). For some reason I have failed to discover, one of them uses FILE *'s and the other uses file descriptors.

[Desktop Entry]
Encoding=UTF-8
Name=Rogue
GenericName=Rogue
Comment=The original curses-based adventure game
Exec=rogue
Icon=rogue.png
Terminal=true
Type=Application
Categories=Game;RolePlaying;
Version=1.0