tag alias: person_over_both_shoulders -> fireman's_carry

create alias person_over_both_shoulders -> fireman's_carry
create alias fireman_carry -> fireman's_carry
create alias firemans_carry -> fireman's_carry

reason: same, though there are very few posts at the moment. if not applicable, requesting a tag move instead and wiki deletion.

EDIT: adding variations to catch possible typos

Done