Support multiple after-tax accounts to better model capital gains

[wscott]

Some people have individual stocks that have been around for many years and have a very small basis. Then they have other savings accounts and what to know if the stock should be sold first or later.

For example: http://forum.mrmoneymustache.com/taxes/wrote-a-retirement-calculator-because-i-orp-com-didn't-do-what-i-want/msg1460616/#msg1460616
(In this example, I don't think the modeling would have mattered much)

We can model multiple after-tax accounts to answer this question. Add this issue to give people a place to request this feature.