path / binary name collisions in ports & base

[Jolan Luff <jolan_(_at_)_cryptonomicon_(_dot_)_org>]

wcobb@ pointed out to me that devel/sdl-ttf installs a "showfont"
binary which also exists in ${X11BASE}/bin.  he suggested resolving
it by renaming it to sdl-showfont (which makes sense to me).

However, I noticed that at least one other port has a collision:
mail/p5-Mail-SpamAssassin's "spamd" binary and Theo's spamd in
/usr/libexec.  (I have /usr/libexec in my path, mostly for locate*
tools)

I remember cdrecord used to not install something (mkisofs?) because
it was previously in base.

Is there a unilateral rule governing this, or is it on a case by
case basis?

- jolan