Move the loading of all ref names for decoration into its own function.
A static variable prevents loading twice, because it's quite expensive.
We can do it this way because we currently never unload decorations.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>