mni.vertex.power.analysis: Compute the statistical power at every vertex
In BIC-MNI/mni.cortical.statistics: Regression analyses on the surface

Given a standard deviation at every vertex this function computes the statistical power both in the form of the n required to recapture a change of delta, or the delta required to recapture a change of n. Basically a wrapper to power.t.test.

1	mni.vertex.power.analysis(std.file, n=25, alpha=0.005, power=0.995, delta=0.5)

`std.file`	A text file with one line per vertex containing the standard deviations at each vertex.
`n`	The number of subjects to compute the power for.
`alpha`	The threshold at which to compute the power.
`power`	The power to use in the computation.
`delta`	The change required in the power computation.