Merge branch 'ab/free-and-null'

A common pattern to free a piece of memory and assign NULL to the
pointer that used to point at it has been replaced with a new
FREE_AND_NULL() macro.

* ab/free-and-null:
  *.[ch] refactoring: make use of the FREE_AND_NULL() macro
  coccinelle: make use of the "expression" FREE_AND_NULL() rule
  coccinelle: add a rule to make "expression" code use FREE_AND_NULL()
  coccinelle: make use of the "type" FREE_AND_NULL() rule
  coccinelle: add a rule to make "type" code use FREE_AND_NULL()
  git-compat-util: add a FREE_AND_NULL() wrapper around free(ptr); ptr = NULL

branch.c

@@ -25,8 +25,7 @@ static int find_tracked_branch(struct remote *remote, void *priv)
 		} else {
 			free(tracking->spec.src);
 			if (tracking->src) {
-				free(tracking->src);
-				tracking->src = NULL;
+				FREE_AND_NULL(tracking->src);
 			}
 		}
 		tracking->spec.src = NULL;