emacs: change binding to suspend current frame
emacs: change binding to suspend current frame

This is the closest analogue of "C-z" in Vim. We have to use
`suspend-frame' instead of `suspend-emacs', because the latter does not
work from terminal emacs when there are other tty frames open, with the
following error:

    There are other tty frames open; close them before suspending Emacs

listx/syscfg,listx/syscfg,listx/syscfg,listx/syscfg,listx/syscfg