more thread-safety measures, particularly for d_ugen.c
more thread-safety enhancements - static variables in g_canvas.c
Fixed errors in previous commit which failed to compile with PDINSTANCE
variables in s_inter.c per-pd-instance so that differnt pd instances can
put sys_startgui wrapper code intended for libpd in s_inter.c - which
s_inter.c to empty out pd-to-GUI queue on startup. Anyhow, ignore
improved order of startup lock setting - class_...
Mods to fix bugs that came to light when syncin...