BUG: Made `setp` accept arbitrary iterables

[madphysicist]

Previously only accepted sequences.

Fixes #6212

[madphysicist]

I don't think the broken Travis test is something I did...

[madphysicist]

Also, while looking through some old code, I found the original use-case where this came up. It's actually not too contrived: pyplot.setp(axes.spines.values(), color='gray'). Fine in Py2, breaks in Py3.

[tacaswell]

There are a transient failures that we have not tracked down yet, restarted the test.

[madphysicist]

While minor, I think you should absorb the doc changes into your PR.

[tacaswell]

I think both of the fixes need to go in. One issue with listifying generators in functions is the side effect, ex

def worker(inp):
    inner = list(inp)
    print("should count to {}".format(len(inner)))


gen_example = (j for j in range(15))

worker(gen_example)
for i in gen_example:
    print(i)

will not behave correctly (you can make this sort of thing work via tee).

[tacaswell]

I am leaning no on backporting unless someone disagrees.

[madphysicist]

That makes perfect sense in this case. As the title indicates, this is not strictly even a bug. If it hasn't been fixed by now, it's been worked around or gone unnoticed. The work-around is simple enough that it doesn't need a backport.