Revise assert_raise to handle any kind of Exception

Ruby's default rescue only handles StandardError subclasses. This is a problem when testing for exceptions that don't inherit from StandardError. The standard timeout library is one such offender: Timeout::Error inherits from Interrupt.

This is causing a test in redis-rb to fail, which is what led me here (see packagethief/redis-rb@b5dd8413203e07f9165f1d51ecec6fffa1ee17dc).

I'm not sure about packagethief@958519aaccfc4d27a574712204508571b42a732f. Prior to this change, these tests were failing due to differences in backtrace formatting (./test/fixtures/failure.rb vs. test/fixtures/failure.rb). If they weren't failing for anyone else, just ignore; it's possible that it's version specific (I tested using 1.8.7 p253).