Put the clock tree connecting wires farther apart from the corona border.

* Bug: In cumulus/plugins.chip.powerplane, while building the connexion
    from the corona border to the root of the HTree, the horizontal
    wire at the top was too close from the border causing a minimal
    spacing error in the DRC. Now put two tracks of distance.

cumulus/src/plugins/alpha/chip/powerplane.py

@@ -539,7 +539,7 @@ class Builder ( object ):
             raise ErrorMessage( 1, 'Cannot build clock terminal as no clock is not known.' )
             return
         for i in range(len(self.conf.coronaCks)):
-            self._connectClock( self.conf.coronaCks[i], i+1 )
+            self._connectClock( self.conf.coronaCks[i], i+2 )
   
     def doLayout ( self ):
         with UpdateSession():