Now editing core/events.lua's buffer_new handler function is no longer necessary
on a per-user basis. If _THEME is set, that theme's buffer.lua is loaded for a
'buffer_new' event, and view.lua for 'view_new'.
Originally the error message was displayed in Textadept, but any attempts to
close the program would fail because core/init.lua wasn't properly loaded.
Errors from 'l_load_script' are displayed in a dialog box now.
