Use PYENV_DEACTIVATE to store which virtualenv has been deactivated (#32)

bin/pyenv-sh-deactivate

@@ -11,12 +11,26 @@ set -e
 
 shell="$(basename "${PYENV_SHELL:-$SHELL}")"
 case "$shell" in
-fish ) echo "functions -q deactivate; and deactivate;";;
-*    ) echo "declare -f deactivate 1>/dev/null 2>&1 && deactivate;";;
+fish )
+  cat <<EOS
+if functions -q deactivate
+  setenv PYENV_DEACTIVATE "\$VIRTUAL_ENV";
+  deactivate;
+end;
+EOS
+  ;;
+*    )
+  cat <<EOS
+if declare -f deactivate 1>/dev/null 2>&1; then
+  export PYENV_DEACTIVATE="\$VIRTUAL_ENV";
+  deactivate;
+fi;
+EOS
+  ;;
 esac
 
 if [ -z "${PYENV_VIRTUALENV_INIT}" ]; then
   # Backward compatibility issue
   # https://github.com/yyuu/pyenv-virtualenv/issues/26
-  echo "pyenv shell --unset"
+  echo "pyenv shell --unset;"
 fi