Use emacs24 for sensible-editor

With the installation of a backported emacs24 package onto
steevie, Emacs 24 is now available on all the Debian systems I
regularly use. Additionally, the previous selection (emacs23) was
causing issues on installations of Sid.

Therefore, select Emacs 24 as the default editor for
sensible-editor.

.selected_editor

@@ -1,2 +1,2 @@
 # Generated by /usr/bin/select-editor
-SELECTED_EDITOR="/usr/bin/emacs23"
+SELECTED_EDITOR="/usr/bin/emacs24"