and incorrect call to cairo_set_source_rgba which is in an unused
function and has no effect except with versions of Tcl less than 8.6
where "load -lazy" is not available and unknown functions cause
immediate exit. Cleaned up remaining references to OpenGL in the
Cairo code, and updated the copyright and acknowledged Chuan Chen, who
coded the Cairo interface. No attempt yet to deal with memory leaks
caused by calling Cairo "create" functions without the accompanying
"destroy" functions.
1d3bb0d698