fixup: correct audio dependencies

I checked our SConstruct file again, apparently I got confused,
we only link libmikmod when making native client builds.

However, it appears that wesnoth does dynamically link lib ogg.
I checked on irc, this was added to support a playlist editor
feature for the map / campaign editor.

https://gist.github.com/cbeck88/f30caf932d5a87bf6ac2
use the homebrew makejobs parameter

I experimented, it appears that scons completely ignores the
makeflags / make jobs environment variables. I couldn't find it in
the documentation, I did find a fink mailing list discussion where
someone claimed this is the case.

http://sourceforge.net/p/fink/mailman/message/31599456/

In any case the experiments using `brew ... -j3` definitely show
that scons doesn't get the memo.
remove oldstable option
remove 'without-x11-driver', which is apparently not a thing
rewrite ccache option text
fixup some comments describing the linkage