[freeciv-ai] final bodyguard cleanup

["Per I. Mathisen" <per@xxxxxxxxxxx>]

This is an updated version of my previous bodyguard cleanup patch. Most of
the previous patch has already been committed as parts of other patches,
so it is quite small now.

Biggest changes:
 - Better/stricter bodyguard checking and handling
 - Cleanup
 - Some new comments
 - Naval bodyguards (need ferry cleanups to work properly, now rarely
   used)
 - Several more sanity checks for bodyguards, no more mech inf
   bodyguarding riflemen
 - Want new bodyguard should ours die

  - Per

bodyguard1.diff
Description: Text document