Section 103. The supreme judicial and superior courts shall have jurisdiction in equity to require the certification of any application for an absent voting ballot which the registrars have unreasonably refused to certify, to order the counting of any ballot improperly rejected, or to enjoin the counting of any ballot which cannot reasonably be identified as the ballot of a person lawfully entitled to vote as provided in sections eighty-six to one hundred and two, inclusive, or which was not cast in accordance therewith; provided, that no proceeding hereunder shall be begun later than the date fixed by law for the final canvass of votes cast for candidates for state offices.