[FEATURE] Support Vagrant 1.6 version command

Vagrant 1.6 introduces a couple new commands, including the `version` command.
The `version` command shows the currently installed version information and
also checks for new updates available.
[FEATURE] Support Vagrant Share

Vagrant 1.5 introduced Vagrant Share to allow remote access to a Vagrant
environment. This adds support for the `share` and `connect` commands.
[FEATURE] Support Vagrant Cloud commands

Vagrant 1.5 added Vagrant Cloud to share boxes. Some boxes
may be protected, the `login` command allows to access those
protected boxes from Vagrant Cloud.
[FEATURE] Support vagrant global-status

Vagrant 1.6 introduced the `global-status` command which allows
to get a quick overview of all active Vagrant environments for the
currently logged in user.
Improve consistency, remove dots at end of command descriptions
Merge pull request #2787 from irnnr/plugin-vagrant

Support new Vagrant commands
prefer virtualenvwrapper_lazy.sh if it is available
allow overriding lib/*.zsh in custom/lib
add npmbrew plugin
don't autocomplete stuff beginning with underscore
Revert "prefer virtualenvwrapper_lazy.sh if it is available"

This reverts commit 08124a0f41e45186c8d64f773936d2389576de31.