use canvas_getrootfor instead of glist_getcanvas, guarantee editor gets created when reloading abstractions

remove redundant call in g_mycanvas.c and filter repeated label updates if
the label hasn't changed as in Pd Vanilla

it works with pd~

Fix bug in which stdout didn't catch on that it should send to parent pd~
in binary; this was caused by different startup order when pd~ was started
with or without GUI (it failed when non-GUI, binary mode).