sbitmap cleanups

[Andrew Haley]

> Date: Mon, 10 Apr 00 15:11:36 EDT
> From: kenner@vlsi1.ultra.nyu.edu (Richard Kenner)
> 
> Are you sure?  I thought with "++", you are guaranteed that it will *not*
> be updated until the sequence point.

Nope.  ANSI, 6.3:

"Between the previous and next sequence point an object shall have its
stored value modified at most once"

"This paragraph renders undefined statement expressions such as

    i = ++i + 1"

Andrew.