[patch] move htab_iterator

[DJ Delorie]

I'm typically against adding things to libiberty "because there's no
other place for them".  The purpose of libiberty is to provide a
portability layer, not a trash can.  However, htab is already in
there, and the argument for putting its accessors there is sound.

However, most of the other functions in hashtab.h are of the form
htab_*().  Could these be changed to match that pattern?  If these
functions are unused, it shouldn't matter to rename them.  (although,
if they're unused, it shouldn't matter to discard them, either)