tree-wide: use coccinelle to patch a lot of code to use mfree()

This replaces this:

        free(p);
        p = NULL;

by this:

        p = mfree(p);

Change generated using coccinelle. Semantic patch is added to the
sources.

src/basic/strv.c

@@ -271,8 +271,7 @@ char **strv_split_newlines(const char *s) {
                 return l;
 
         if (isempty(l[n-1])) {
-                free(l[n-1]);
-                l[n-1] = NULL;
+                l[n - 1] = mfree(l[n - 1]);
         }
 
         return l;