MIDI import: set default pitch bend range to +/-2 semitones

AFAIK, this is how the General MIDI standard says it should be.

plugins/MidiImport/MidiImport.cpp

@@ -249,6 +249,8 @@ public:
 				it->setName( tn );
 			}
 			lastEnd = 0;
+			// General MIDI default
+			it->pitchRangeModel()->setInitValue( 2 );
 		}
 		return this;
 	}