Policies are read once during server startup and subsequently
managed through in memory map. In-memory map is updated as
and when there are new changes coming in.
* Added ErrPolicyNesting which is returned when nesting of policies has occured
* Replaces ErrMalformedPolicy in the case of nesting
* Changed test case in bucket-policy-parser_test.go (ErrMalformedPolicy -> ErrPolicyNesting)
Harshavardhana