enhanced 'Mean' attribute on vcs plots

[doutriaux1]

fix #1024
use %.4g rather %.f for both prettyness and 'last-digits-may-change-on-some-machnies' reasons
use cdutil where possible to produce a better average

[doutriaux1]

@aashish24 @painter1 @dlonie we should be good to merge this.

goes with:
CDAT/uvcdat-testdata#19

[painter1]

LGTM except that there seems to be a "print" statement left over
from a debugging session.
On 2/10/15 3:40 PM, Charles Doutriaux
  wrote:



  @aashish24 @painter1
    @dlonie we should be good to merge
    this.
  goes with:
    UV-CDAT/uvcdat-testdata#19
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[doutriaux1]

doh! Nice catch!
fixed