extendBuff( aura, duration ) function for cleaner code

[syrifgit]

Instead of writing buff.metamorphosis.expires = buff.metamorphosis.expires + 8

You'd write extendBuff( "metamorphosis", 8 )

Works with negative numbers, a check for the buff being removed if negative extension is greater than remaining duration, breaks out on 0.

Thoughts? What else am I missing to polish this up if you're interested in having it?

I copied it from addstack, unsure if I actually need the local a = class.auras[ aura ]?