contourc.m: Code special case for meshgrid input (30X performance increase). * scripts/plot/contourc.m: Check input vectors x,y for being uniform grid and skip interp2 re-mapping if possible. Rename output 'cout' to 'c' to match documentation. Preserve idx as a range, rather than a matrix, to use less memory.

6057744acd2c71c069a4b171c5fe1ff0d86c9e5f gnulib-hg