environment/factory option to skip sanity checks

[leventov]

In production, it is crucial to have an option like Launcher.skipSelfChecks = true, which

• disables AstParentConsistencyChecker
• disables contract check in CtElement.equals/hashCode
• disables contract signature checks in CtTypeImpl.addMethod() (however, as I mentioned here: Replace CtClass.constructors model from Set to List #646 (comment) this check is always at least not useful, sometimes harmful)

[monperrus]

I'm OK with such an option, however, we would keep the checks enabled by default.

[leventov]

Yes, of cause default setting should checks=on.