py3: handle keypresses in chistedit stable

py3: handle keypresses in chistedit

Now you can navigate and change the action for a commit. You can also
reorder commits, as long as that doesn't result in a conflict (then it
crashes).

Differential Revision: https://phab.mercurial-scm.org/D7182

--- a/hgext/histedit.py	Thu Oct 31 14:25:51 2019 -0700
+++ b/hgext/histedit.py	Thu Oct 31 14:46:17 2019 -0700
@@ -1608,7 +1608,7 @@
                 renderhelp(helpwin, state)
                 curses.doupdate()
                 # done rendering
-                ch = stdscr.getkey()
+                ch = encoding.strtolocal(stdscr.getkey())
         except curses.error:
             pass