add definition for ubuntu 13.04 (server)
break up postinstall.sh
install libdbus and fix typos on VirtualBox Guest additions
remove existing VirtualBox guest additions before installing new version
remove ruby and rubygems source after installing them
add /opt/ruby/bin to the global path
Merge pull request #677 from ngpestelos/ubuntu-13-04

add definition for ubuntu 13.04 (server amd64)
Allow installation with obsolete gpg keys
Merge pull request #681 from rds13/master

Fix problem building VM for Debian 5.X from archive.debian.org
Update Debian 6.0.7 ISO URLs
Fix install instructions for old Debian ISOs
Merge pull request #683 from paulhammond/debian-iso-urls

Fix Debian 6.0.x ISO URLs
replace global postinstall.sh script by dedicated scripts
Merge pull request #684 from rds13/master

Replace global postinstall script by dedicated scripts
Added debug statement when probed TCP port is already used.
Call before_boot and after_postinstall hooks if available.
Added build hooks:
* before_create, after_create, after_up, 
* wait_ssh_enabled, after_command_sequence, after_postinstall
Tiny formatting fixes.
Load a definition only once and cache it afterwards.
This is required to maintain state in the definition.
E.g. toggling a flag in the build hooks.
* Prevent environment reinitialization.
* Made (current) provider accessible from environment.
* Made box accessible from the definition.