Fix colormap functions when N is not of class double (bug #44070) * autumn.m, bone.m, cool.m, copper.m, cubehelix.m, gray.m, hsv.m, ocean.m, rainbow.m, spring.m, summer.m, winter.m: cast N to double since in this colormap functions, N is used directly used in the operations and ends up casting colormap to something else. Note that a colormap MUST be of class double. Also, if N is an integer class, all values in colormap end up 0 or 1. Also simplify code for input checking by declaring default on function signature line. * flag.m, gmap40.m, hot.m, jet.m, lines.m, pink.m, prism.m, white.m: simplify input check like the other colormap functions. * test/colormaps.tst: add new test file to test all colormaps at once. * test/Makefile.am: add new test file to build system. used to create the colormap and if less