Update vagrant completion with "plugin" subcommand

This subcommand was added in Vagrant 1.1.

src/_vagrant

@@ -12,6 +12,7 @@
 # -------
 #
 #  * Nikita Fedyashev (https://github.com/nfedyashev)
+#  * Mark Cornick (https://github.com/markcornick)
 #
 # ------------------------------------------------------------------------------
 
@@ -24,6 +25,7 @@ _1st_arguments=(
     'help:[TASK] Describe available tasks or one specific task'
     'init:[box_name] [box_url] Initializes current folder for Vagrant usage'
     'package:Packages a vagrant environment for distribution'
+    'plugin:Manage plugins'
     'provision:Run the provisioner'
     'reload:Reload the vagrant environment'
     'resume:Resumes a suspend vagrant environment'
@@ -44,12 +46,20 @@ _box_arguments=(
     'repackage:NAME Repackage an installed box into a `.box` file.'
 )
 
+local -a _plugin_arguments
+_plugin_arguments=(
+    'install:NAME Install a plugin to the system'
+    'license:NAME LICENSE_FILE Add a license for an installed plugin'
+    'list:Lists all installed plugins'
+    'uninstall:NAME Uninstall a plugin from the system'
+)
+
 __task_list ()
 {
     local expl
     local -a tasks
 
-    tasks=(box destroy halt init package provision reload resume ssh ssh_config status suspend up version)
+    tasks=(box destroy halt init package plugin provision reload resume ssh ssh_config status suspend up version)
 
     _wanted tasks expl 'help' compadd $tasks
 }
@@ -59,6 +69,11 @@ __box_list ()
     _wanted application expl 'command' compadd $(command ls -1 $HOME/.vagrant/boxes 2>/dev/null| sed -e 's/ /\\ /g')
 }
 
+__plugin_list ()
+{
+    _wanted application expl 'command' compadd $(command vagrant plugin list 2>/dev/null| cut -d' ' -f1)
+}
+
 __vm_list ()
 {
     _wanted application expl 'command' compadd $(command grep Vagrantfile -oe '^[^#]*\.vm\.define *:\([a-zA-Z0-9]\+\)' 2>/dev/null | cut -d: -f2)
@@ -89,8 +104,33 @@ __vagrant-box ()
     esac
 }
 
+__vagrant-plugin ()
+{
+    local curcontext="$curcontext" state line
+    local -A opt_args
 
+    _arguments -C \
+        ':command:->command' \
+        '*::options:->options'
 
+   case $state in
+       (command)
+           _describe -t commands "gem subcommand" _plugin_arguments
+           return
+       ;;
+
+       (options)
+           case $line[1] in
+               (license)
+                   _arguments ':feature:__plugin_list' '*:file:_files'
+               ;;
+               (uninstall)
+                   _arguments ':feature:__plugin_list'
+               ;;
+           esac
+       ;;
+    esac
+}
 
 local expl
 local -a boxes installed_boxes
@@ -117,6 +157,10 @@ case $state in
       (box)
           __vagrant-box
       ;;
+
+      (plugin)
+          __vagrant-plugin
+      ;;
       (up|provision|package|destroy|reload|ssh|halt|resume|status)
 	_arguments ':feature:__vm_list'
     esac