t / t4135 / diff-plain.diffon commit try_remove_empty_parents(): teach to remove parents of reflogs, too (a8f0db2)
   1--- postimage.txt.orig  2010-08-18 20:13:31.432002255 -0500
   2+++ postimage.txt       2010-08-18 20:13:31.432002255 -0500
   3@@ -1 +1 @@
   4-preimage
   5+postimage