MAINT: Factor talib tests out to separate file.
MAINT: Make talib an optional dependency. Fixes #362.
MAINT: Log more information on history update failure.

Log the field and algo datetime when the update of the return frame
fails; re-raise the error until the when and why of the value error is
understood.
Merge pull request #382 from quantopian/talib_optional

Make talib an optional dependency.
ENH: Add new order statuses for broker integration
BUG: Clean up handling of reject() and hold() orders
TST: Add tests for behavior of rejected/held orders.

Also made a tweak to the handling of Order.status
for when a held order is filled (partial or full).
ENH: Re-work the usage of _status on Order