add 2 subclasses of RuntimeException, one to be thrown when there is a mistake in the arguments for a job, and one to be thrown when something is not supported in the current mode. although runtime exceptions are typically not supposed to be caught/handled this allows for nicer error messages to the user if one of these 2 errors is thrown (for example this could be done in Tool, not yet implemented)
pass message for new RuntimeException subclasses into super constructor
Merge pull request #860 from tresata/feat-exceptions

add 2 subclasses of RuntimeException, one to be thrown when there is a m...
Merge branch 'develop' of https://github.com/twitter/scalding into develop