log_first_n implementation doesn't match doc, ignores formatting args

The log_first_n doc says:

`Logs 'msg % args' at level 'level' only first 'n' times`

However, the implementation only tracks the caller's file and line number, and ignores the formatting args. So if I do something like:

```
for arg in ['arg1', 'arg2']:
log_first_n('%s', 1, arg)
```

It will never log for arg2.