[TW] Core/Spells: Los for few aoe spells

http://www.truewow.org/forum/viewtopic.php?f=78&t=12641
- Blizzard, Rain of fire, Hurricane and Volley, now checks targets are
in los of the center of the spell
- Bladestorm now goes through normal effect los check
- Shadowfury and Flamestrike targets selected from los of center of
spell and not the caster
- Flamestrike persistent damage only target players in los of center
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- More general check could be made to fix more spells but most likely break others so that's why it just has spell id switch