Exception#==

Specs fixed:

Exception#==
- returns true if one exception is the dup'd copy of the other
- returns true if both exceptions have the same class, no message, and no backtrace
- returns true if both exceptions have the same class, the same message, and no backtrace
- returns true if both exceptions have the same class, the same message, and the same backtrace
- returns true if the two exceptions inherit from Exception but have different classes
- returns true if the two objects subclass Exception and have the same message and backtrace
- returns false if the two exceptions differ only in their backtrace
- returns false if the two exceptions differ only in their message
Merge pull request #685 from krekoten/exception_equal_value

Exception#==