Overhaul errorbar family of functions. * scripts/plot/errorbar.m: Add %!error tests for input validation. * scripts/plot/private/__errcomm__.m: Correctly validate that numeric inputs are numeric. More precise error reporting indicating the problematic argument. * scripts/plot/private/__errplot__.m: Fix automatic color cycling for matrices with multiple columns of data. Check "yerr" case first in if/elseif trees since it is the most common. Pull static computations out of for loop for performance.