All proceedings of such cities and towns as herein included, heretofore had, subsequent to the adoption of section 696-b [SS 15] by the thirty-sixth general assembly, and prior to the passage of this Act,* providing for the issuance of bonds within the limitations of this Act, for the purchase or erection of garbage disposal plants, the vote of the people authorizing such issue and the bonds issued under such proceedings and vote, are hereby legalized and declared legal and valid, the same as though all of the provisions of this Act had been included in said section 696-b of the supplemental supplement to the Code, 1915, and such cities may issue and sell such bonds without again submitting such question to vote.