When printing a diff report in NMT, we print out the diff for the totals too:

```
Total: reserved=19838567KB +1572932KB, committed=2741843KB +1573020KB
```

It would be helpful if we would print out the diff for the two sub sections ("mmap" and "malloc") too, at least for the latter.

Something like this:
```
Total: reserved=19838567KB +1572932KB, committed=2741843KB +1573020KB
       malloc: 524290KB +524288KB #67108865 +67108864
       mmap: reserved=18219740KB, committed=1123016KB
```