Expanded user validation fields to accept up to 255 chars

Hi MrJuliuss! I [chatted with you a couple weeks ago](http://forums.laravel.io/viewtopic.php?pid=65623#p65623) about increasing the number of characters allowed for things like passwords. I know you said you'd handle it, but I ran a ```composer update``` and broke my login again, so I thought I'd try to help.

The patch expands the allowed length of passwords and names in User.php to 255 chars. I've tested it locally, and it works with my site. 

I also checked the migrations in Syntara and Sentry, and they're both using the default ```->string()``` for those fields with no limit explicitly set. In MySQL < 5.0.3, that's means a max size of 255 chars, 65536 chars after. Postgres 8.3+ has a VARCHAR limit up to 1GB, and SQL Server 2005+ can handle a 2GB VARCHAR. Not sure about other databases, but 255 chars should hopefully be fine for them, too.

It's a pretty straightforward change, but let me know if you have any questions or concerns.

Thanks again for Syntara,
Matthew / KingMob