[Eeglablist] setting a common 'powbase'

[Toby Fernsler]

"Amplitude" was a poor choice of words, I meant the (complex) 
time-frequency coefficients, and not their absolute value. 
Typically what people do when running timef.m for the purposes of 
comparing conditions is to run it once to get the 'powbase' output for 
each dataset, then average that across conditions to get the grand 
average 'powbase', then rerun timef.m with the new 'powbase' specified 
in the function call.
Toby