- Add missing dependency for playing music: USE_LINUX+=openal-soft
- In the `do-extract', rather than changing current directory, pass it to
tar(1) as a -C argument and don't needlessly use semi-private _DISTDIR
variable: this makes the command shorter and avoids bogus double slash
in the build log
- Provide more user-friendly wrapper script which anticipates potential
problems that typically affect running this program and advises on how
to solve them
- Spell GNU/Linux correctly in the COMMENT and port description; reformat
the latter with `fmt -w 75' for better looks (less ragged right edge)