Capture any type of exception in a 'raises' block

The current way of handling the exceptions in a raises block only
captures exceptions inheriting StandardError which is the default
for rescue IIRC.

Not sure if this is intended behaviour though. This patch changes it
so that **all** the exceptions are rescued by the block.

Code example exhibiting current behaviour:

    class MyException < Exception; end

    # raises block will not rescue MyException breaking tests
    #
    raises MyException, 'something happened' do
      raises MyException.new
    end