fix nfs mount fail with freebsd.
Add --no-parallel to provision
document common validation pattern
Automatically enable symlinks on vboxsf for VirtualBox 4.1 (see #713 and 387692f9c8fa4031050646e2773b3d2d9b2c994e).
Merge pull request #2414 from Schpidi/symlinks_vb41

provider/virtualbox: automatically enable symlinks on vboxsf for VirtualBox 4.1
Update CHANGELOG
Merge pull request #2412 from maxlinc/config_validation

website/docs: document '_detected_errors' pattern in plugin configuration guide.
website/docs: clearer
website/docs: update to support 4.3.x
Merge pull request #2404 from canausa/patch-1

commands/provision: add --no-parallel
Update CHANGELOG
Merge pull request #2400 from hikch/master

guests/freebsd: fix nfs mount fail with FreeBSD9.1 (synced_folder).
Update CHANGELOG
core: improved commenting in bin/vagrant