Use select.poll instead of select.select in SocketServer.BaseServer.serve_forever

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-09-27.11:24:44.981>
labels = ['library', 'performance']
title = 'Use select.poll instead of select.select in SocketServer.BaseServer.serve_forever'
updated_at = <Date 2017-09-28.15:05:48.447>
user = 'https://bugs.python.org/bboneva'

bugs.python.org fields:

activity = <Date 2017-09-28.15:05:48.447>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-09-27.11:24:44.981>
creator = 'bboneva'
dependencies = []
files = []
hgrepos = []
issue_num = 31610
keywords = []
message_count = 4.0
messages = ['303127', '303247', '303251', '303254']
nosy_count = 3.0
nosy_names = ['vstinner', 'giampaolo.rodola', 'bboneva']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue31610'
versions = []