performance attribution does not work correctly when percentages are passed in

[twiecki]

We need a flag that says whether positions are in $ or %. Calling get_perc_alloc() on % does not work.

[vikram-narayan]

@twiecki what do you think about making get_percent_alloc return the input as is, if the input is already in %?

[twiecki]

Question is if we can detect that reliably.

[vikram-narayan]

ah gotcha. I'll add a flag which does that, and defaults to dollars

[vikram-narayan]

added this flag to to the risk exposure plot PR: #433