AI retasking units back and forth

[elexis]

Has been reported by gameboy here ​http://wildfiregames.com/forum/index.php?showuser=13978 and here #3580.

You can reproduce the bug with r17181 and replaying the attached commands.txt.

The bug occurs with the red units at minute 11/12 near the stone at the very right.

The AI orders the units to gather, then walk, waits some turns, orders them to gather stone and repeats that.

Seems like it can't decide what to do.

[mimo]

In 17185:

petra: only units which have effectively started an attack should be stopped when the attack is aborted, fixes #3582

[mimo]

Thanks for reporting.