fileinfo: File lists for plots with several columns

Macro add_01 creates lists of plots that contain data from several
files with a suffix -V## to denote column numbers.  The new macro
plot-V01 creates lists of data files that are needed for each plot.
histogram: Exact dependencies for plots

Plots now only require data files that are really needed.
correlation: Exact dependencies for plots

Plots now only require data files that are really needed.