Improve python output support

Improve python output support
fix some bugs

base/statistics.cc:
    -  Move the python dump stream stuff into the statistics package
    because it needs more control over the file when there
    are multiple dumps
    -  add a subname to the output
    -  make all of the stats a list instead of variable arguments to
    get around the 255 argument limit
    -  the description needs to be triple quoted
    -  avoid errors for formulas that don't have any root element
    set up.
base/statistics.hh:
    -  get rid of mode_python and just separate python dumping from
    regular stats dumping
    -  fix a huge bug that made a Formula use a VectorData instead
    of a FormulaData

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extra : convert_revision : 7303cff3ccdcc3d306ab17375219fc7fecac7e5e