sbitmap cleanups

[Richard Kenner]

    The result of evaluating ((*ap++ | *bp++) != *bp) is not well defined.
    It can be evaluated may different ways all equally valid. The problem
    is the use of *bp++ and *bp in the same expression without an
    intervening sequence point.

Are you sure?  I thought with "++", you are guaranteed that it will *not*
be updated until the sequence point.  But I agree this is probably a
bad iea due to the confusion.

    Perhaps it should be written as follows which matches the style of many of
    the other routines.

They are all this way now ...