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

sha1_file.c

@@ -611,8 +611,7 @@ char *compute_alternate_path(const char *path, struct strbuf *err)
 
 out:
 	if (seen_error) {
-		free(ref_git);
-		ref_git = NULL;
+		FREE_AND_NULL(ref_git);
 	}
 
 	return ref_git;