bug#21102: 24.5; prompt of `read-char' obscured by keystroke echo

[Emilio Lopes]

Start Emacs with "emacs -Q" and type the following in the "*scratch*" buffer:

  (read-char "char: ")

With the point after the right paren type now "C-x C-e"
(`eval-last-sexp').  If you press this key-sequence slowly, waiting one
second (the value of `echo-keystrokes') between "C-x" and "C-e" the
prompt string ("char: ") will be obscured by the echo area showing the
keystrokes "C-x C-e-" (note the trailing dash!).

In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
 of 2015-04-15 on xz
Windowing system distributor `The X.Org Foundation', version 11.0.11604000
System Description:    Debian GNU/Linux 8.1 (jessie)

Configured using:
 `configure --without-compress-install --with-zlib --with-imagemagick
 --with-xml2 --with-svg --prefix=/usr/local/stow/emacs-24.5'

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LC_CTYPE: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction