faster paste

We don't need to perform the scroll calculations after inserting every
single character from the clipboard.

README.md

@@ -73,10 +73,10 @@ found anything amiss: http://akkartik.name/contact
 * Undo/redo can be sluggish in large files. If things get sluggish, killing
   the process can lose data.
 
-* Large files may grow sluggish in other ways. Pasting more than a line or two
-  gets slow. I've noticed in 100KB files that closing the window can take a
-  few seconds. And it seems to take longer in proportion to how far down my
-  edits are. The phenomenon persists even if I take out undo history.
+* Large files may grow sluggish in other ways. I've noticed in 100KB files
+  that closing the window can take a few seconds. And it seems to take longer
+  in proportion to how far down my edits are. The phenomenon persists even if
+  I take out undo history.
 
 * The text cursor will always stay on the screen. This can have some strange
   implications:

main.lua

@@ -428,24 +428,22 @@ function App.keychord_pressed(chord)
     local before = snapshot(before_line)
     local clipboard_data = App.getClipboardText()
     local num_newlines = 0  -- hack 1
+--?     print(Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)
     for _,code in utf8.codes(clipboard_data) do
       local c = utf8.char(code)
       if c == '\n' then
         Text.insert_return()
-        if (Cursor_y + Line_height) > App.screen.height then
-          Text.snap_cursor_to_bottom_of_screen()
-        end
         num_newlines = num_newlines+1
       else
---?         print(Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)
         Text.insert_at_cursor(c)
-        if Cursor_y >= App.screen.height - Line_height then
-          Text.populate_screen_line_starting_pos(Cursor1.line)
-          Text.snap_cursor_to_bottom_of_screen()
---?           print('=>', Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)
-        end
       end
     end
+    App.draw()
+    if Cursor_y >= App.screen.height - Line_height then
+      Text.populate_screen_line_starting_pos(Cursor1.line)
+      Text.snap_cursor_to_bottom_of_screen()
+--?       print('=>', Screen_top1.line, Screen_top1.pos, Cursor1.line, Cursor1.pos, Screen_bottom1.line, Screen_bottom1.pos)
+    end
     -- hack 1: if we have too many newlines we definitely need to scroll
     for i=before_line,Cursor1.line do
       Lines[i].screen_line_starting_pos = nil