Airspy controller - changes method for adjusting center tuned frequency

when tuner channels are allocated by the airspy.  New method determines
the min/max requested frequency range and sets tuner center to the
center of that range, while limiting the total usable bandwidth to 90%
of the bandwidth, to account for rolloff of 5% at the upper/lower edges.

When a new channel is requested, if the channel fits within the current
center frequency and usable bandwidth, the center tune frequency is not
adjusted, to minimize the number of retunes on a busy system.

src/controller/channel/Channel.java

@@ -714,7 +714,7 @@ public class Channel extends Configuration
 			}
 			catch( SourceException se )
 			{
-				mLog.info( "Couldn't obtain source for channel [" + mName + "]" );
+				//Do nothing, we couldn't get a source for the channel
 			}
 		}
 	}