Suggestion: Allow AT enhancements to be slotted in alternate slots if already slotted elsewhere

[mgretzin]

If you have an AT enhancement, e.g., Superior Defiant Barrage: Accuracy/Damange, slotted in a power, and you switch to the alternate slots (shift-click), you can't slot slot the non-superior version of the enhancements. Likewise, you can slot the enhancement in the alternate slots of another power to test what it would do there. These enhancements should work the same way as purple set enhancements do.