Add options to plots.py and example for thickness evaluation
Refine plot functions in plots.py and add alternate_columns_from_tables() to io_table.py
Clean up __main__ example in plots.py

Plot scan-rescan thickness values from table (alternating columns)
Fixed a nibabel-related freesurfer label bug in annot_to_vtk():

        The 'True' flag in nibabel.freesurfer.read_annot(annot_file, True)
        gives the original FreeSurfer label values, not the FreeSurferColorLUT
        labels, and when set to 'False' assigns all otherwise unlabeled
        left cortical vertices to 3, which is also assigned to the caudal
        middle frontal gyrus.  To correct this ambiguity, this program assigns
        -1 to all vertices with label 0 in the original ('True') labels.
Merge branch 'master' of github.com:binarybottle/mindboggle