BUG: DatetimeIndex with time as key
BUG: Option context applies on __enter__

Option context no longer overrides options when used outside a `with`
statement.

Added test TestConfig.test_option_config_scope

Closes #8514
Merge pull request #8925 from hkleynhans/fix/8514_option_context_with

BUG: Option context applies on __enter__
BUG: fix doctests in pandas.core.common

$ nosetests pandas/core/common.py --with-doc -v
Merge pull request #8907 from behzadnouri/time-slice

BUG: DatetimeIndex with time object as key
Merge pull request #8931 from rupertthompson/fix/core_common_doctests

BUG: fix doctests in pandas.core.common
CLN: adding encoding lines to all files in test
Merge remote-tracking branch 'upstream/master'