Proposal: make portsnap generate INDEX-${OSREL:R} only by default

Hi,

Currently the default portsnap.conf would generate INDEX-11, INDEX-10
and INDEX-9.  The INDEX file is only used for searching ports, and only
one (INDEX-${OSREL:R}) file is actually used.

Traditionally, we create all supported INDEX-* files by default, but the
only users who would benefit from this default are the ones who shares
ports tree across many systems that runs different FreeBSD releases.
 And even in these scenario, it's likely that they would still want to
tweak the configuration, as we may be creating more than needed INDEX-*
files.

So for simplicity and to reduce cycles wasted on everyone's system, I'd
propose the attached change to head/'s portsnap.conf and similar changes
to stable/9 and stable/10's portsnap.conf so that only INDEX-${OSREL:R}
is created by default.  Users who want additional INDEX files can
uncomment the corresponding lines.

Any objections/concerns?  I'll commit the change if no objection is
raised in a week.

Cheers,
-- 
Xin LI <delphij_at_delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die