mv: allow a single source with --target-directory

[ilkecan]

It should be possible to move a single file if target-directory is given.

I couldn't find a way to set min_values conditionally so I set it to 1 and then manually check that it's not 1 unless target-directory is used.

[sylvestre]

it seems like an unrelated change, no ?

[ilkecan]

That variable is created to avoid "temporary value dropped while borrowed" error:

  --> src/uu/mv/src/mv.rs:79:41
   |
79 |       let mut app = uu_app().after_help(&*format!(
   |  _________________________________________^
80 | |         "{}\n{}",
81 | |         LONG_HELP,
82 | |         backup_control::BACKUP_CONTROL_LONG_HELP
83 | |     ));
   | |     ^ - temporary value is freed at the end of this statement
   | |_____|
   |       creates a temporary which is freed while still in use
84 |       let matches = app
   |                     --- borrow later used here
   |
   = note: consider using a `let` binding to create a longer lived value
   = note: this error originates in the macro `format` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0716`.
error: could not compile `uu_mv` due to previous error

[sylvestre]

oh, right, thanks