Comment 3 for bug 1660591

Reverting the following commit makes the crash go away.

commit 951d0e82aa562f05c4b7859a2906aee7bc2e8639
Author: Jorgen Loland <email address hidden>
Date: Thu Oct 10 13:55:38 2013 +0200

    Bug#17405466: USE_COUNT: WRONG COUNT FOR KEY AT 0X27547278,
                  3 SHOULD BE 4

    Consider an index (kp1, kp2, kp3), and a WHERE clause involving
    all three keyparts ('kpx_pred' represents a predicate usable by
    the range access method on keypart 'x'):

    "WHERE (kp2_pred OR kp2_pred) AND
            kp3_pred AND
           (kp1_pred OR kp1_pred)"

    The range optimizer first creates a SEL_ARG tree for kp2 with
    two SEL_ARGs, then another SEL_ARG tree for kp3. Both SEL_ARGs
    for kp2 will point to this kp3-SEL_ARG via the next_key_part
    pointer. The use_count of the root of the SEL_ARG tree for
    kp2 is now 1 (it is pointed to by SEL_TREE::keys[]), and
    the use_count of the root of the SEL_ARG tree for kp3 is 2
    (next_key_part pointers from both kp2 SEL_ARGs).

    Now the range optimizer creates a SEL_ARG tree with two
    SEL_ARGs for kp1. Both these need to point to the SEL_ARG tree
    for kp2 via the next_key_part pointer. This should increase the
    use_count of the kp2 SEL_ARG tree by 1 (+2 next_key_part
    pointers for the kp1 SEL_ARG tree, -1 since SEL_TREE::keys[]
    now points to the kp1 SEL_ARG tree and not directly to the
    kp2 SEL_ARG tree).

    This increase in use_count also needs to be propagated to the
    kp3 SEL_ARG tree, and this is where the bug was: instead of
    increasing the use count for each next_key_part pointing to
    the kp3 SEL_ARG tree, only the next_key_part of the root of
    kp2 SEL_ARG tree was increased. The fix is to propagate the
    increase to all SEL_ARG trees pointed to by all SEL_ARGs.

    Debugging this without printing the full SEL_ARG range trees
    would have been very hard. The patch therefore also adds a
    parameter to print_tree() so that a full printout is done when
    printing to the debug trace but not when printing to optimizer