Bug#722644: say explicit package name or my()

[jidanni at jidanni.org]

Also here perhaps say instead "explicit package name or my()".

$ cat r.pl
use warnings FATAL => 'all';
use strict;
$u++
$ perl r.pl
Global symbol "$u" requires explicit package name at r.pl line 3.
Execution of r.pl aborted due to compilation errors.