Sqlite3cache: default to using a db per bin

Author: gwaldron

src/osgEarthDrivers/cache_sqlite3/SQLite3Cache

@@ -28,10 +28,17 @@ namespace osgEarth { namespace Drivers
         virtual ~SQLite3CacheOptions() { }
 
     public:
+        //! Location of the cache files
         OE_OPTION(std::string, rootPath);
+
+        //! Number of threads to devote to background cache writing
         OE_OPTION(unsigned, threads, 2u);
+
+        //! Tiemout (milliseconds) when trying to local a db
         OE_OPTION(unsigned, busyTimeout, 5000u);
-        OE_OPTION(bool, separateBins, false);
+
+        //! Whether to use a separate .db for each CacheBin
+        OE_OPTION(bool, separateBins, true);
 
     public:
         virtual Config getConfig() const {