Hello,

Rainy day today, so I decided to squash one of the long-outstanding
items on my TODO list; merging ibuffer-occur into replace.el.  

This patch adds two new functions: `multi-occur' and
`multi-occur-by-filename-regexp'.  `occur' basically becomes a special
case of `multi-occur'.  It also attempts to expose an API
(`occur-engine') for modes which have multiple buffers to use for
defining their own occur-like functionality; I know at least one person
who has wanted this.

Anyone have any objections to this going into CVS?