Make <logpath> work with relative directories

At the moment <logpath> works only with full paths, doesn't work with relative paths.
It would be nice to have it work from the working directory of the .exe

Working:

``` xml
<logpath>C:\Program Files\My Service\logs</logpath>
```

Not working:

``` xml
<logpath>logs</logpath>
```

``` xml
<logpath>%CD%\logs</logpath>
```

Thanks,
Andrea
