Yes, the symbols will compare as different

```
>>> Symbol('i', dummy=True)==Symbol('i')
False
```

But 

1) this is still a bad idea to use symbols that you don't know whether they are clashing with something already present. It's possible that someone trying to do the same thing used a symbol named 'i' with the assumption of 'dummy' being True. So I am -1 to the use of Symbol('i').

2) in spirit of the recently removed `prep` option, this public, undocumented parameter should probably be removed.

> can still be useful when debugging code interactively

You have mentioned this more than once...what is it that is problematic with the Dummy?

If it is a need to test if one expression equals another except for Dummies, I think we need to deal with this another way. I made a suggestion in #1322 about how this could be handled by wrapping dummies to the same dummy symbol. We already have special functions in the testing suite for handling various problems. I think it would be good to upgrade that to handle situations like this. (But that need not be part of this PR.)