Don't show login info in verbose mode

[jaimeMF]

Currently it will print the password if the --password option is given, it should be hidden.

$y-dl --username foo --password 1234
[debug] System config: []
[debug] User config: ['--keep-video', '--verbose', '--write-info-json', '--write-thumbnail']
[debug] Command-line args: ['--username', 'foo', '--password', '1234']
[debug] youtube-dl version 2013.07.18
[debug] Git HEAD: de7a91b
[debug] Python version 2.7.5 - Darwin-11.4.2-x86_64-i386-64bit
[debug] Proxy map: {}
Usage: y-dl [options] url [url...]

y-dl: error: you must provide at least one URL

I would also hide the username.