Put binaries in /usr/games and support $DESTDIR
Look for the IWADs in /usr/share/games/doom in addition to $CWD
Check for not-logging before writing to the log file

Fixes a segfault when the $CWD is on a read-only filesystem.
Convert deutex.6 to UTF-8

This could possibly cause issues with non-GNU roff implementations,
but for now I have a hard time finding the 7-bit ASCII clean escape
equivalents, so I'm calling this "Good Enough".
Recognise the Freedoom IWAD names