intersect canvas rect and painter clip rect for curve polygon clipping


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@2117 29e17f8d-cf37-471e-a288-72cc03a76eda
doxygen docs added for new type of color maps


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@2120 29e17f8d-cf37-471e-a288-72cc03a76eda