It turns out the ia64 architecture's disc2 overflows if we put the
ports/ tree on it. This makes putting the ports/ tree on disc2 at
all dependent on the NOPORTREADMES knob as well as the NOPORT knob
(at the moment NOPORT may be set while NOPORTREADMES isn't, that
should probably be revisited). And it hardcodes ia64 for NOPORTREADMES
by request the ia64 release builder.

While here really get rid of the temp file 'make index' leaves behind.

Tested by: i386 and ia64 'make release'
Reviewed by: marcel
MFC after: 1 day