Any person who has exclusive possession and control of irrigable land under a purchase contract, which purchase contract has been approved by the district, and in connection with which any incremented value to be paid to the United States has been paid in full, shall be considered the owner of such land for the purpose of qualifying such purchaser to vote in voting districts outside of the municipality, and the vendor of the land covered by such contract shall not be entitled to vote as the owner of such land. This section shall not apply to lessees whose lease contains an option to purchase, unless and until such option to purchase shall have been exercised.