This gets called after saving a file to assure that it be executable.
You can set the absolute or relative mode in variable `executable-chmod' for
After saving, if the file is not executable, set this mode.
This mode passed to `set-file-modes' is taken absolutely when negative, or
relative to the files existing modes. Do nothing if this is nil.
Typical values are 73 (+x) or -493 (rwxr-xr-x).