* pass `QEmacsState` to key grab functions
* clear `grab_key_opaque` when freeing windows, buffers, mode_data
* add checks on window and buffer pointers in key grab functions
* this should fix a crash bug when deleting unsynched buffers from bufed
* fix `reload_buffer` to update buffer `file_size` and `mtime` fields
* check buffer file before invoking commands that modify the buffer
* check buffer file after command that changes the current window
or the current window's buffer
6fb16e1cc2