stats python fixes for dealing with vectors better. graph tweaking

stats python fixes for dealing with vectors better.  graph tweaking
ipkb stat and formulas from the command line.

util/stats/info.py:
    no need to raise an attribute error if two values aren't found
    in the exact same set of runs.  Would be good to check that each
    run is the same though.
util/stats/stats.py:
    more graph tweaking
    command to execute a formula from the command line.
    add interrupts per kilobyte of data

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extra : convert_revision : 78d6b14d340d08edcbc69e4c1c5a4c1dd9bb10dd