Identify "android" user-agent as a remote client in transcode_needed()

While doing the performance tests with Retune as remote client, i noticed a lot of log messages like (actually this gets logged for each song during the request for the songlist):

```
[2014-12-28 06:33:51]    xcode: Determining transcoding status for codectype mpeg
[2014-12-28 06:33:51]    xcode: User-Agent: RetuneAndroid
[2014-12-28 06:33:51]    xcode: Could not identify client, using default codectype set
[2014-12-28 06:33:51]    xcode: Codectype supported by client, no transcoding needed
```

In transcode.c the remote clients are only identified if they contain "remote" in the user-agent string. In http_daap.c there is an additional check for "android". I added this check to the transcode_needed() function.