drop default param from Fraction::Fraction

because if I make call-sites use the default, I get warnings about
ambiguous functional conversions

Change-Id: Ifd452c946832d0f9d62a10a46d90fe1ea3e79945

include/tools/fract.hxx

@@ -39,7 +39,7 @@ public:
                     Fraction();
                     Fraction( const Fraction & rFrac );
                     Fraction( Fraction && rFrac );
-                    Fraction( long nNum, long nDen=1 );
+                    Fraction( long nNum, long nDen );
                     Fraction( double dVal );
                     ~Fraction();