bug#24563: kill-region fails while dragging a selection

[Phil Ruffwind <rf@rufflewind.com>]

Emacs 25.1 seems to have changed the behavior of doing kill-region (C-w)
while dragging a selection in GUI mode.  Here are the steps to
reproduce:

 1. Run Emacs in GUI mode via: emacs -Q
 2. Type: M-x set-variable mark-even-if-inactive nil
 3. Open a file containing some text.
 4. Make a selection using the mouse, but do NOT release the mouse
    button.
 5. Type: C-w.

In Emacs 24.5, this would initially do nothing, but pressing C-w a
second time will kill the selected region correctly.

In Emacs 25.1, this fails with "The mark is not active now" and
deselects the region.

Had I turned mark-even-if-inactive back on, it would cause the
previously selected region to be killed instead, which can lead to lots
of accidental killing.

Naturally, one wouldn't do this on purpose: one should release the drag
before doing C-w, but it's very easy to accidentally overlap the two
operations when done in haste.

---

In GNU Emacs 25.1.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.20.9)
 of 2016-09-18 built on juergen
Windowing system distributor 'The X.Org Foundation', version
11.0.11804000
System Description:     Arch Linux

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

Important settings:
  value of $LC_COLLATE: C
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

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