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).

However, we still need to figure out if we want to supress gui_canvas_getscroll
when suppressing the scrollbars. Currently it still gets called, which will
adjust the viewport to make objects at negative indices visible. I think
instead we want to anchor the viewport to 0,0 at top left and supress those
calls to get a nice speedup in the GUI.

commit: 619f056b3f39e04e482d04854c1c166de2621d64