Rename helper memor to indicate usage.

Expected argument is a Property protobuf.
Factor out value_pb bits from '_get_value_from_property_pb'.
Add support for 'list_value' field of a Value protobuf.

Fixes #223.

Manually lands Tagtoo@0475d5e, included by mistake in PR #126.
Kowtow to pylint's over-fussy 'too-many-return-statements'.

Incorporates feedback from @dhermes.
Merge pull request #246 from tseaver/223-marshal_list_values

Fix #223: marshal list values from protobufs
DRY definition of _Monkey class used for testing.

Move to a non-testcase module, to avoid dependencies between testcases.
Merge pull request #250 from tseaver/refactor-dry_monkey

DRY definition of _Monkey class used for testing.
Merge branch 'master' into 239-remove_pragma_no_cover
Merge with master to pick up PR #250.