vchoi_fork

[svn-r12644] Description:
    Improve density of the B-tree further.  For greater depths of B-trees,
the gains are over 100%...

    Also, don't split internal nodes with 3->4 splits, use a 1->2 split
instead, so that the density of the nodes around a split is maximized.

Tested:
    Mac OS X/PPC 10.4 (amazon)
    Linux/32 2.6 (chicago)
    Linux/64 2.6 (chicago2)