if we've got a tree of type ALWAYS or MAYBE.


sql/opt_range.cc:
  BUG#15448 (group_min_max test failure): Don't buypass group-min-max optimizer entry point 
  if we've got a tree of type ALWAYS or MAYBE.
  The effect observed by this bug has been introduced by this cset: 
  ChangeSet 1.1967.5.2 2005/12/26 08:40:09 sergefp@mysql.com. The cset introduced PARAM::remove_jump_scans
  which purpose was to avoid making [always unsuccessful] attempts to construct index_merge for construct 
  index_merge for conditions like "t.key1partX=c1 OR t.key1partY=c2". The effect of this change was that some
  queries that previously had produced a SEL_TREE representing candidate for index_merge(X,Y) now started to 
  produce SEL_TREE with type=ALWAYS, and group-min-max analysis for these trees has been bypassed.
  In this fix we make SEL_TREE with type=ALWAYS to be processed in the same way as (SEL_TREE*)NULL, its equivalent.