add zsh completion support, courtesy of Ted Leung

--HG--
extra : convert_revision : svn%3A98f53aa3-d424-0410-b225-a548b0275c4d/Projects/virtualenvwrapper/trunk%401850

Author: dhellmann

virtualenvwrapper_bashrc

@@ -146,14 +146,19 @@ function workon () {
 # Set up tab completion.  (Adapted from Arthur Koziel's version at 
 # http://arthurkoziel.com/2008/10/11/virtualenvwrapper-bash-completion/)
 # 
-_virtualenvs ()
-{
-    local cur="${COMP_WORDS[COMP_CWORD]}"
-    COMPREPLY=( $(compgen -W "`show_workon_options`" -- ${cur}) )
-}
 
-complete -o default -o nospace -F _virtualenvs workon
-complete -o default -o nospace -F _virtualenvs rmvirtualenv
+if [ -n "$BASH" ] ; then
+    _virtualenvs ()
+    {
+        local cur="${COMP_WORDS[COMP_CWORD]}"
+        COMPREPLY=( $(compgen -W "`show_workon_options`" -- ${cur}) )
+    }
+
+    complete -o default -o nospace -F _virtualenvs workon
+    complete -o default -o nospace -F _virtualenvs rmvirtualenv
+elif [ -n "$ZSH_VERSION" ] ; then
+    compctl -g "`show_workon_options`" workon rmvirtualenv
+fi
 
 # Path management for packages outside of the virtual env.
 # Based on a contribution from James Bennett and Jannis Leidel.