Add fail_with() stub and move Failure from Exploit
Remove Failure (moved to parent class)
Switch to Failure vs Exploit::Failure
[Fix RM 8224] - undefined method `include?' for nil:NilClass

Bug due to registry_enumkeys returning nil.
Missed these little devils
Land #2229 - Re-implement fail_with() function
Land #2230, enum_shares nil deref

[FixRM #8224]