Interest constructor: Make _mustBeFresh True by default. Refs #1333.
tests: In test_encode_decode_interest, for the freshInterest test setMustBeFresh(False) since True is now the default. Refs #1333.
Merge branch 'issue/1333-MustBeFresh-default-True'. Refs #1333.
http://redmine.named-data.net/issues/1333