BUG: allow series to use gcf-style figures

[cpcloud]

cc @fonnesbeck

here's the original issue: 51cc9d9#commitcomment-3494266

[cpcloud]

@fonnesbeck can u try this out? @jreback any thoughts?

[cpcloud]

@jreback couple of things here: possible issue is the new-ish API change that if figure and by are given an error will be raised saying that you cannot pass figure and by since the figure will be discarded with grouped hist plots; i feel like this is something @wesm might give a big 👎 to...personally i would prefer to get an error telling me my passed figure won't be used. OTOH i could certainly make _subplots take a figure argument.

[cpcloud]

@jreback can we get this in to 0.12?

[jreback]

is what Series.plot does (take from the current figure)?

[cpcloud]

yep

[jreback]

looks reasonable

[cpcloud]

actually what i said was slightly wrong: nothing is done with the figure unless the current axis has ticks on the right yaxis.

[wesm]

this looks fine to me

[cpcloud]

will merge after failing test fix