Negative numbers should be allowed optionally for InputNumber in currency mode

[larrysimon]

There should be an option to allow a currency field to accept a negative number. This is a common use case for an amount field, for example, to offset a previously entered amount which was wrong.

[larrysimon]

Clarification: I see now that negative numbers can be entered if the field is empty. I thought they couldn't be entered at all because I couldn't add a minus sign to the amounts already in the fields on the pInputNumber demo page. It seems reasonable that a person should be able to add the minus sign after they entered the number. They may have entered a number with lots of digits then realize they forgot the negation and shouldn't have to type it all over again.