Added: Option to exclude app-specific caches from backups.

I've seen some apps abuse their cache, letting them grow to over 500MB and taking up a ton of unnecessary space in backups.  Also, the Android developer docs state that the contents of the cache can be deleted at any time (http://developer.android.com/guide/topics/data/data-storage.html#filesInternal), so no app should be relying on anything in there, and thus it shouldn't be necessary to include the caches in the backup.

And, some apps use non-standard cache locations.  While it would be cumbersome to special-case exclusions for many such apps, its worthwhile to do so for a few of the biggest consumers -- for my devices / usage, that's Firefox and TuneIn.