Make the function to check if a unit fulfills a requirement
 vector more reusable

 - Move it to common requirement code
 - Make it easy to support other universal kinds

Reviewed by Emmet Hikory <persia>

See patch #4558

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24814 a0f10bec-cc02-0410-94fc-a9cfff90b4cd