use precise64 box as box_url

it's given as config.vm.box too, so we'll use precise64 from files.vagrantup.com.

this might be especially useful in case hhvm is going to be used some day.
add redis-server & php5-redis
Mention Xdebug in README.md
Mention Redis-Server in README.md
Merge pull request #7 from hexa2k9/hotfix/box_url

use precise64 box as box_url
Merge pull request #5 from hexa2k9/update-readme

Mention Xdebug in README.md
Merge pull request #6 from hexa2k9/feature/redis-server

add redis-server & php5-redis