patch 7.4.751

Problem:    It is not obvious how to enable the address sanitizer.
Solution:   Add commented-out flags in the Makefile. (Dominique Pelle)
            Also add missing test targets.

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    751,
 /**/
     750,
 /**/