Introduce the notion of CompiledPolicy to hold stuff that
remains immutable during evaluation - e.g. rules, function,
schedules etc
Cloning takes about 60 nano seconds for an engine loaded with
ACI policies. Earlier it used to take 40 microseconds.
Thus there is easily more than 100x speedup.
Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>