put iemgui and canvas dialogs near the place where the popup menu appeared, and center the other dialogs

the last commit deleted the old flext files. I didn't realize git automatically puts deleted files with a commit, otherwise I would have done this all in a single commit

add defines for sys_open, sys_close, sys_fopen and sys_fclose as placeholders until the code to handle utf-8 filenames on Windows gets ported

remove old *.tcl files (except for pd.tk, as there are a few procs there we may want to keep for reference for awhile)

(I forgot to actually test the branch that handles strings with quotes in them)

for garrays we disable editing gl_x1 and gl_x2. They get set automatically to show the entire array by default. May want to revisit array viewport later, but for now this keeps the bug from happening.

allow this to work:
gui_start_vmess("foo", "");
gui_start_array();
gui_s("hello");
gui_end_array();
gui_end_vmess();

In other words, a gui message with a single array argument. There should rarely be a need for this (if at all), but it should still send a well-formed message to the GUI (which it wasn't before this bug fix)