add workaround for out-of-order request from Pd that tries to destory a border on a scalar it already told us to erase

first try at get the copyfromexternalbuffer logic ported. This allows to paste Pd source code into a patch

comment out some sys_vgui calls which are _probably_ no longer necessary (plus extra comments saying as much)

update open dialog window height/width/font/fontsize for iemguis as they are resized/repositioned with the mouse

disable canvas menu options when the dialog is present. Also, change variable name "o" to something less error-prone

Give window focus when asking if we need to save before closing. Using a (possibly buggy) "restore" method instead of the more obvious "focus" method, so this needs more testing

fix iemguis and canvas scalehandle to track mouse position instead of delta-- this fixes a bug when the mouse goes below the minimum dimensions. Plus, some more cleanup of the scalehandle code

restore the ability to show multiple iemgui label handles at once, and use class instead of id to identify them

use <dialog> modal instead of javascript prompt. Also, port some changes from Vanilla to allow closing window immediately after saving

remove pdtk_check_scroll_on_motion for the time being. (Not sure it's needed, but can revisit if necessary)