8130115: REDO - Reduce Symbol::_identity_hash to 2 bytes Summary: Convert Symbol::_identity_hash from integer to short integer to save two bytes. Also change identity_hash() to have 'this' and first two bytes of symbol join the calculation. Reviewed-by: iklam, coleenp, shade

^build/
^dist/
^drop/
^drop_included/
^webrev
/nbproject/private/
^.hgtip