Volume.cc: message maps

the diffstat speaks for itself.
ok!

hm, which of the multiple styles used in Volume.cc should i adopt?  is it
```
if ...
{
    ...
}
```
or
```
if ...
    {
    ...
    }
```
or
```
if ... {
    ...
}
```
?  all these styles are used in the file, do you have any idea which one is the most recent?