* src/virsh.c: Adjust some vshCmdOptDef command option flags
to improve auto-generated help command syntax.

* src/virsh.c: ... now that info is generated.

* src/virsh.c: Now, every command must have a "desc" string,
even if it has zero length.  Mark these, so they'll be filled in.

* src/virsh.c: Also, diagnose extra arguments after --help (-h).

Daniel