BUG: Remove output arg before calling run_pipeline

The IPython magic still created an output file because
the output argument was only removed after the pipeline
was run. This fix simply removes the argument before
the call to run_pipline() when running the IPython magic.
BUG: Apply integer truncation to order amounts earlier in the pipeline.

Truncate non-integer order amounts in `TradingAlgorithm.order` instead of
`Blotter.order`.  This fixes an issue where non-integer orders coming out of
order_value can spuriously trigger a `LongOnly` trading guard.

Example:

sid.price == 2.0
order_value(sid, 5) -> order(sid, 2.5) -> truncated to order(sid, 2.0)
order_value(sid, -5) -> order(sid, -2.5) -> LongOnlyViolation b/c 2.0 - 2.5 < 0
BLD: Set scipy back to 0.12.0

The internal system used to build and get burn-in on packages was
accidentally using scipy 0.12.0, despite the change in the requirements
file to 0.13.2

Setting back to using scipy 0.12.0 until 0.13.2 is more tested with
internal systems, with the goal of upgrading to >= 0.14.0 as soon as
possible.
MAINT/TEST: Move `to_utc` from `history_cases.py` to `test_utils.py`.
DOC: Tweaks to docstrings in `history.py` and `history_container.py`.
ENH: Add `freq_filter` argument to `HistoryContainer.update_digest_panels`.

Adds a new argument, `freq_filter`, to `HistoryContainer.update_digest_panels`,
which can be used to supply a predicate determining which digest panels are
updated by the call.  This is useful for supporting initialization/backfilling
of multi-frequency panels in subclasses.
ENH: Add removal of elements in benchmark.
BUG: RollingPanel was not behaving correctly in corner cases.

There quite some bugs in certain corner cases. Dropping of obsolete
axes was not working correctly, roll over could cause obsolete axes
to not drop. The tests are much more stringent now as well.