oops, forgot to rm caller's arg when function param was removed
minor
short circuit report generation for scanning/fs errors
modify error handling for tests

make separate callbacks for afterScanning and afterLinting,
since they are invoked with different parameters and made
the code look confusing.

also, prevent further callback invocation after some errors,
since cli does process.exit(), but the unit tests don't.
tests & fixtures
modify error handling for tests
reporter test, hack to test console logging