Add support for integer data types for image cdata. * gl-render.cc (draw_image): Add support for 'single' data type by converting FloatNDArray to GLfloat. * graphics.cc (convert_cdata_2): Change function signature to add is_real parameter. Convert data from 1-based indexing to 0-based indexing only if is_real is true. * graphics.cc (convert_cdata_1): Change function signature to add is_real parameter. Pass is_real through to convert_cdata_2. * graphics.cc (convert_cdata): Change CONVERT_CDATA_1 macro to support IS_REAL argument. Pass IS_REAL through to convert_cdata_1. Add support for uint16 data type. * image.m: Remove hack converting all integer cdata to single data type.

gnulib-hg = gnulib-hg