I'd rather add a second macro adding a prefix (putting __FILE__ and __LINE__ in here like suggested in #237) instead of changing the output of the normal DEBUG, because there might be split multi-line DEBUG statements like
```C
DEBUG("foo was %d", foo);
foo = foobar;
DEBUG(" and is now %d\n", foo);
```
or using DEBUG with progress information like
```C
DEBUG(".");
```