Help is usually printed from tools if no arguments are given and there
is not default action. However "gio mount" and "gio trash" just silently
return. Let's print "No locations given" error and show help consistently.
"gio help COMMAND" shows some arguments with "..." and some with "…",
which looks weird, e.g.:
$ gio help mount
gio mount [OPTION…] [LOCATION...]
Let's use "…" consitently.
This command collects the various commandline utilities that
are currently shipped in gvfs, and unifies them under a single,
command-style binary.
The tools just use GIO APIs, so it makes sense for them to live here.
