'trapped creatures' do not use defensive spells

[GoogleCodeExporter]

Creatures without a ranged attack that cannot reach the creature attacking them 
will not use the spells they have available.

To reproduce: Place a level 10 hero knight on an island in lava and have an 
Archer attack the knight. The knight does not engage in combat and will not 
enable rebound or heal but will slowly die. If he uses his spells correctly he 
would have won the 'fight'.
Notice he will use the spells once you throw one of your own creatures on the 
island.

Reproduced on r1589

Related to issue #495

Original issue reported on code.google.com by Loobinex on 4 Feb 2015 at 12:23

[GoogleCodeExporter]

With heal, wind and fly covered in Issue #495, that only leaves 'rebound', 
'invisibility' and 'armour' as defensive spells creatures should use when they 
are being attacked but cannot counterattack.

Original comment by Loobinex on 17 Apr 2015 at 10:01