man: flowtop: Make wording in description for --version consistent

Make the wording consistent with the other man pages.

This was probably messed up by my previous commit which was not properly
split.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
astraceroute: Mention exit after printing information in built-in help

Mention the fact that astraceroute exits after printing either the help
of the version information.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
curvetun: Mention exit after printing information in built-in help

Mention the fact that curvetun exits after printing either the help of
the version information.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>