Update gnuplot plotting scripts for faster or more modern synta * scripts/plot/__gnuplot_drawnow__.m: Use default values in function header. Check number of arguments to function immediately. Use single quotes to avoid lots of backslashing. Use strtok() to replace hand-coded functionality. Initialize persistent variables in declaration (10% faster). * scripts/plot/gnuplot_binary.in: Replace tabs with spaces. Simplify input validation. Add %!test block. * scripts/plot/private/__gnuplot_get_var__.m: Use default values in function header. Use "*char" in fread to automatically convert to char variable. * scripts/plot/private/__gnuplot_ginput__.m: Check immediately for required version of gnuplot. Use "*char" in fread to automatically convert to char variable. Use fputs in place of fprintf to match rest of code. * scripts/plot/private/__gnuplot_has_feature__.m: Initialize persistent varibles in declaration. Use false () rather than logical (zeros()) construction. * scripts/plot/private/__gnuplot_has_terminal__.m: Use strtok() to replace hand-coded functionality * scripts/plot/private/__gnuplot_print__.m: Replace sprintf calls with direct string char matrix concatenation (2.4x faster) where possible. Replace for loop with multiple argument form of set(). Use single quotes to avoid lots of backslashing. * scripts/plot/private/__gnuplot_version__.m: Use single quotes to avoid lots of backslashing.