demand slapindex after slapd.conf += index

[Hallvard B Furuseth <h.b.furuseth@usit.uio.no>]

A suggestion for a vain attempt to kill a FAQ:

To teach people to run sbin/slapindex after adding an index to
slapd.conf, slapd can refuse to start if an index file is missing but
dn2id.bdb exists.  Same with other slap tools that need to open/create
the index file.  (At least slapadd, I don't know if there are others.)

slapindex and slapcat, at least, will need to keep working.

If database recovery can sabotage this feature or vice versa, recovery
will of course have to take precedence.

-- 
Hallvard