Semi-Merge commit '749fa78' into cg_merges_20130619a (one instance in modminer)

Conflicts:
	driver-avalon.c
	driver-bflsc.c
	driver-bitforce.c
	driver-icarus.c
	driver-modminer.c

driver-modminer.c

@@ -792,6 +792,7 @@ static void
 modminer_fpga_shutdown(struct thr_info *thr)
 {
 	free(thr->cgpu_data);
+	thr->cgpu_data = NULL;
 }
 
 static char *modminer_set_device(struct cgpu_info *modminer, char *option, char *setting, char *replybuf)