zsh: Add venv function

This enables or lists virtual environments

.zsh/functions/Makefile

@@ -2,6 +2,6 @@ DESTDIR:=$(DESTDIR)/functions
 objects=chpwd_show_todo chpwd_update_git_vars env get_cnt line \
 	precmd_maybe_festival precmd_update_git_vars precmd_update_updates \
 	preexec_update_vars prompt prompt_git_info rprompt \
-	update_current_git_vars welcome
+	update_current_git_vars welcome venv
 
 include ../../dotfiles.mk

.zsh/functions/venv

@@ -0,0 +1,15 @@
+# -*- mode: sh; -*-
+if [ "${#}" -eq 1 ]; then
+    venv_activate="$HOME/.virtualenv/$1/bin/activate"
+
+    if [ -r "$venv_activate" ]; then
+        source $venv_activate
+    else
+        echo "$1 is not a know virtual environment"
+    fi
+else
+    echo "Virtual environments: "
+    for itm in ~/.virtualenv/*; do
+        echo "  $(basename $itm)"
+    done
+fi