[Kernel] Add tests for Exiting and Exception functions

[sampersand]

This PR adds tests for Kernel.{abort,exit,exit!,at_exit} and Kernel.{throw,catch,raise,fail}, as well as slightly tweaking the fail signature.

Additionally, it adds in the assert_send_type_error method (which is just a direct copy of assert_send_type, but accepts a type as the second argument)

[sampersand]

Checking for a value like SystemExit rather than a type seems to be testing behavior, not the type.

The idea is to make sure that the exception that was thrown was one we expected from exit, not something like ArgumentError/TypeError caused by invalid arguments