Khan/khan-exercises — pull request #26083 by beneater (2012-07-13 18:14:25+00:00)
Title: Add custom problem types for custom stack test

This adds some custom problem types to a few fractions exercises that always ask the same specific question. The new problem types have `data-weight="0"` so they don't show up normally, but can be referenced in a custom stack.

[Card 1](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/recognizing_fractions_0.5.html?debug&problem=custom-1)
[Card 2](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/recognizing_fractions_0.5.html?debug&problem=custom-2)
[Card 3](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/recognizing_fractions_0.5.html?debug&problem=custom-3)
[Card 4](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/recognizing_fractions_0.5.html?debug&problem=custom-4)
[Card 5](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/adding_fractions_with_common_denominators.html?debug&problem=custom-5)
[Card 6](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/recognizing_fractions_0.5.html?debug&problem=custom-6)
[Card 7](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/equivalent_fractions.html?debug&problem=custom-7)
[Card 8](http://sandcastle.khanacademy.org/media/castles/beneater:custom-stack-test/exercises/adding_fractions.html?debug&problem=custom-8)

@tomyedwab @xymostech review?