crecord: re-center display in interactive curses commit on pageup/down

A long-standing issue in the crecord (interactive curses commit interface)
is that using PageUp/Down to move along longer-than current screen size
chunks would "lose" the cursor and not properly re-center.

There has been self.recenterdisplayedarea() to do that, but it has not been
in use for some reason. Add calls to the appropriate uparrowshiftevent()
and downarrowshiftevent() methods to fix this.

mercurial/crecord.py

@@ -671,6 +671,7 b' class curseschunkselector(object):'
             nextitem = currentitem
 
         self.currentselecteditem = nextitem
+        self.recenterdisplayedarea()
 
     def downarrowevent(self):
         """
@@ -710,6 +711,7 b' class curseschunkselector(object):'
             nextitem = currentitem
 
         self.currentselecteditem = nextitem
+        self.recenterdisplayedarea()
 
     def rightarrowevent(self):
         """