Colin Greenwood says band are looking forward to 'dark' headlining set
Guitarist says the group is trying to help musicians and fans
Thom Yorke alludes to teen star's temper tantrum
They get together under the 'Featured Artist Coalition' banner
See the band preparing to play '15 Step'
'I'm gonna ruin them!' declares the teen star
Director 'McG' says Yorke might contribute
Band hope music will encourage people to donate money to Shelter
But Chris Brown's arrest overshadows proceedings
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