common: bitset_set

common: bitset_set

This bitset_set change relaxes policing of bitset_set, so that
out-of-range can be queried in the contains interface. This means
that callers cam simplifiy calls.  For example:

 if (key == invalid) || !set.contains(key)) {
  do_stuff
 }

 becomes

  if (!set.contains(key)) {
   do_stuff
  }

Signed-off-by: Alex Ainscow <aainscow@uk.ibm.com>