Hi,

While endian-neutralising mandocdb(8), I noticed that it broke with the 
last series of commits: the manual type (mdoc, man, cat) wasn't 
accounted for when pruning the database.

The enclosed patch takes account for this.  It also adds some in-line 
documentation.  It also removes the "verb > 1" parts, which I find a 
little unnecessary (they can be added back in).

Thoughts?

Kristaps

P.S., I noticed that mandoc.db grows a little each time `-d' is run over 
it with the same keys (mandoc.index does not).  I'll look carefully to 
see if we're letting anything stay in there.