[freeciv-ai] Time to enemy city/unit

[Gregory Berkolaiko <Gregory.Berkolaiko@xxxxxxxxxxxx>]

Attached is a patch which separates very similar calculations from:
  find_something_to_kill
  kill_something_with
  process_attacker_want
into 2 new functions
  time_to_enemycity/unit
which provide an estimate of the time required to reach city/unit.

This helps to squash an old bug where spped was compared to build cost...

Also, I provide a new function which allows to get the type of the boat the
player would be able to build, thus getting rid of some hardcoded values,
guesses and checks.

The above will change the behaviour but not visually.

This is the first step in my quest for unification of the above three functions.

Will be committed quite soon unless there are objections.

G.

time_to_enemy.diff
Description: Text document