py3: use integer division in curseschunkselector.printstring()

This fixes a crash when scrolling in curses UI when refresh() is called
when a float value (namely 'self.firstlineofpadtoprint', taking its
value indirectly from 'self.linesprintedtopadsofar').

mercurial/crecord.py

@@ -1156,7 +1156,7 b' class curseschunkselector(object):'
 
         # is reset to 0 at the beginning of printitem()
 
-        linesprinted = (xstart + len(t)) / self.xscreensize
+        linesprinted = (xstart + len(t)) // self.xscreensize
         self.linesprintedtopadsofar += linesprinted
         return t