bz2: BZ2File should expose compression level as an attribute

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-07-04.20:01:33.695>
labels = ['type-feature', 'library']
title = 'bz2: BZ2File should expose compression level as an attribute'
updated_at = <Date 2016-09-04.08:33:02.244>
user = 'https://bugs.python.org/joshtriplett'

bugs.python.org fields:

activity = <Date 2016-09-04.08:33:02.244>
actor = 'joshtriplett'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2016-07-04.20:01:33.695>
creator = 'joshtriplett'
dependencies = []
files = []
hgrepos = []
issue_num = 27450
keywords = []
message_count = 5.0
messages = ['269806', '269818', '272756', '274348', '274349']
nosy_count = 4.0
nosy_names = ['joshtriplett', 'r.david.murray', 'martin.panter', 'xiang.zhang']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27450'
versions = ['Python 3.6']