Disable Returns Receiver Checker by default when running Resource Leak Checker

[msridhar]

Right now, the Returns Receiver Checker (RRC) runs by default as a subchecker of the Resource Leak Checker (RLC), since the RLC extends the Called Methods Checker. This has a significant runtime cost, and provides little benefit in the common case. We should instead not run the RRC as a subchecker of the RLC by default, but allow it to be enabled with a command-line option.

[msridhar]

As a temporary workaround, the RLC can be run with the parameter -AdisableReturnsReceiver to disable the RRC.