virtualbox: use local VBoxGuestAdditions.iso by default

fixes #1123
updated docs
Add null builder reference to Docs
Correct example to use ssh_username/ssh_password
Merge pull request #1133 from stonith/master

website: Null Builder docs were missed
Update docs.erb
builder/vmware-vmx: add floppy_files support

fixes #1057
Merge pull request #1136 from rasa/1057-add-floppy-files-to-vmware-vmx

builder/vmware-vmx: add floppy_files support
Update platforms.html.markdown

Added Parallels
common: add test for empty val
Merge pull request #1132 from rasa/1123-use-local-vboxguestadditions-iso

virtualbox: use local VBoxGuestAdditions.iso by default
Update CHANGELOG
Force LANG=C before appending rest of environment, as only first occurence is used
Merge pull request #1145 from jsoriano/fix-env-order-lang-c

Force LANG=C before appending rest of environment