(QCmatrix, QCcolor_adjustment, QCmask, Qemboss)

(QCmatrix, QCcolor_adjustment, QCmask, Qemboss)
(Qedge_detection, Qheuristic): New symbols.
(syms_of_xfns): Initialize new symbols.
(lookup_image): Handle `:mask X', `:algorithm emboss', and
`algorithm (edge-detection ...)'.
(xbm_format, xpm_format, pbm_format, png_format, jpeg_format):
(tiff_format, gif_format, gs_format): Add `:mask'.
(XBM_MASK, XPM_MASK, PBM_MASK, PNG_MASK, JPEG_MASK, TIFF_MASK)
(GIF_MASK, GS_MASK): New enumerators.
(x_laplace_read_row, x_laplace_write_row): Functions removed.
(emboss_matrix, laplace_matrix): New variables.
(x_to_xcolors, x_from_xcolors, x_detect_edges, x_emboss)
(x_edge_detection): New functions.
(x_laplace): Rewritten in terms of x_detect_edges.
(x_build_heuristic_mask): If image has a mask, free it.