interpreter checkpoint.

interpreter checkpoint.
  * generate different versions of binary operators
    for each size of int and float, so that proper
    truncating happens after each operation to
    simulate the various sized ops.
  * add slice expressions
  * publish World.CompileStmtList, CompileDeclList, CompileExpr
  * handle type-less expressions in CompileExpr

R=austin
DELTA=1459  (1327 added, 11 deleted, 121 changed)
OCL=34382
CL=35581