This is first cset for WL#1394 "Optimize index merge when all involved index ranges include only values with equal keys"
The main idea is to exploit the fact that key scans for "key=const" return ordered sequences of rowids.


include/my_base.h:
  Added HA_EXTRA_KEYREAD_PRESERVE_FIELDS flag
include/my_bitmap.h:
  Added a couple of utility functions
include/my_sys.h:
  Added my_conunt_bits_ushort function
innobase/include/row0mysql.h:
  Added support for HA_EXTRA_KEYREAD_PRESERVE_FIELDS
innobase/row/row0sel.c:
  Added support for HA_EXTRA_KEYREAD_PRESERVE_FIELDS
mysys/my_bit.c:
  Added my_count_bits_ushort function
mysys/my_bitmap.c:
  Added a couple of utility functions
sql/ha_berkeley.cc:
  Added cmp_ref rowid comparison function.
sql/ha_berkeley.h:
  Added cmp_ref rowid comparison function.
sql/ha_heap.h:
  Added cmp_ref rowid comparison function.
sql/ha_innodb.cc:
  Added cmp_ref rowid comparison function and support from HA_EXTRA_KEYREAD_PRESERVE_FIELDS
sql/ha_innodb.h:
  Added cmp_ref rowid comparison function.
sql/handler.h:
  Added cmp_ref rowid comparison function.
sql/opt_range.cc:
  Added QUICK_ROR_{INTERSECT,UNION}_SELECT classes and related optimizer code
sql/opt_range.h:
  Added QUICK_ROR_{INTERSECT,UNION}_SELECT classes
sql/sql_delete.cc:
  Changed to use new ROWID comparison function
  also always call quick->reset() for quick selects
sql/sql_select.cc:
  Account for new quick select types
sql/sql_select.h:
  New, proper rowid ordering/comparison function to be used with Unique class etc.
sql/sql_test.cc:
  Account for new quick select types
sql/sql_update.cc:
  Account for new quick select types