Merge lp://qastaging/~lapsu/graphite/holtwinters into lp://qastaging/~graphite-dev/graphite/main

Wow, this looks terrific. Thank you for implementing this (and very cleanly I might add). This is also a great motivation for me to finally break out functions.py into a package instead of keeping it a gigantic module.

I'm in the process of digging out of a large backlog of graphite project duties so I may not get this merged in for a couple days but I will definitely merge it in for the next release.

Sorry for the delayed response, I've finally reviewed your branch and the code definitely looks good but in testing I ran into a couple issues. First there seems to be a missing import of 'from datetime import timedelta' in functions.py as some of the new code uses timedelta. Second I got the following stacktrace when rendering http://graphite/render/?target=holtWintersForecast(carbon.agents.muon.avgUpdateTime)

Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/django/core/handlers/base.py", line 100, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/opt/graphite/webapp/graphite/render/views.py", line 101, in renderView
    seriesList = evaluateTarget(requestContext, target)
  File "/opt/graphite/webapp/graphite/render/evaluator.py", line 10, in evaluateTarget
    result = evaluateTokens(requestContext, tokens)
  File "/opt/graphite/webapp/graphite/render/evaluator.py", line 21, in evaluateTokens
    return evaluateTokens(requestContext, tokens.expression)
  File "/opt/graphite/webapp/graphite/render/evaluator.py", line 29, in evaluateTokens
    return func(requestContext, *args)
  File "/opt/graphite/webapp/graphite/render/functions.py", line 687, in holtWintersForecast
    analysis = holtWintersAnalysis(series, bootstrap)
  File "/opt/graphite/webapp/graphite/render/functions.py", line 614, in holtWintersAnalysis
    last_seasonal = getLastSeasonal(i)
  File "/opt/graphite/webapp/graphite/render/functions.py", line 569, in getLastSeasonal
    return bootstrap['seasonals'][j]
IndexError: list index out of range

Context from the last frame:
i = 0
j = -1440
season_length = 1440
seasonals = []
boostrap['seasonals'] = TimeSeries(name=seasonals, start=1310247240, end=1310330040, step=60)

Very useful change when it's finally implemented :)

I'd be happy to re-review if anyone can fix the current issue. Once it passes a little testing it'll be merged into trunk.