errno.h header is required now that errno is a per-thread variable.
"undefined symbol 'errno'" at runtime with dlopen()'d modules.

--- backend/snapscan-sources.c.orig	Wed May 18 14:00:59 2016
+++ backend/snapscan-sources.c	Wed May 18 14:01:15 2016
@@ -1,3 +1,5 @@
+#include <errno.h>
+
 /* sane - Scanner Access Now Easy.
 
    Copyright (C) 1997, 1998, 2002, 2013 Franck Schnefra, Michel Roelofs,