PR 1886/cpukit
* sapi/include/rtems/rbtree.h, sapi/inline/rtems/rbtree.inl,
score/include/rtems/score/rbtree.h,
score/inline/rtems/score/rbtree.inl, score/src/rbtree.c,
score/src/rbtreeinsert.c: This patch enables inserting duplicate keys
into rbtree. It is possible to turn on this feature when initializing
the tree.