Fixed a bug when paging the summary.

BUGS

@@ -6,8 +6,6 @@ Current
   the timed out status when un-paused.
 - Tmp files are being left behind after shutdown.
 - All tools in AppImages aren't working correctly. See ./vigil --self_test
-- When paging the summary window the cursor line should stay in the same
-  place on the screen.
 - Sometimes git_blame produces an error, depending on characters in its
   input.
 
@@ -252,6 +250,8 @@ Fixed
   is a glitch in the scrolling.
 - When paging the summary window, with the bottom scroll bar showing, the
   cursor line drifts up or down a row.
+- When paging the summary window the cursor line should stay in the same
+  place on the screen.
 
 
 Won't fix

vigil/__main__.py

@@ -336,7 +336,7 @@ class Summary:
         return self._highlight_cursor_row(
             self._view_widget.appearance(dimensions), cursor_y)
 
-    def mouse_scroll(self, dx, dy):
+    def scroll(self, dx, dy):
         scroll_x, scroll_y = self._view_widget.position
         dy = min(dy, scroll_y)
         self._view_widget.position = scroll_x, scroll_y - dy
@@ -375,15 +375,11 @@ class Summary:
 
     def cursor_page_up(self):
         view_width, view_height = self._view_widget.portal.last_dimensions
-        x, y = self._cursor_position
-        jump = view_height - 1
-        self._cursor_position = (x, max(y - jump, 0))
+        self.scroll(0, view_height)
 
     def cursor_page_down(self):
         view_width, view_height = self._view_widget.portal.last_dimensions
-        x, y = self._cursor_position
-        jump = view_height - 1
-        self._cursor_position = (x, min(y + jump, len(self._column) - 1))
+        self.scroll(0, -view_height)
 
     def cursor_home(self):
         x, y = self._cursor_position
@@ -796,7 +792,7 @@ class Screen:
             last_x, last_y = self._last_mouse_position
             dx, dy = x - last_x, y - last_y
             if self._is_summary_focused:
-                self._summary.mouse_scroll(dx, dy)
+                self._summary.scroll(dx, dy)
             else:
                 self._move_listing((-dx, -dy))
         else:  # Mouse press