video: fix --no-aspect

This also affects the --aspect option and the "aspect" property.
manpage: document --aspect special values

Use of these is "discouraged", but they're there to select these special
cases with the "aspect" property. They really should use some sort of
choice option type, but since it would be some work to make these work
with float values, the simple and dumb alternative was picked.
manpage: fix Lua script shutdown description again

It was split at the wrong sentence.

Also, sneak in a reference to mp.suspend.