"show location of pointer" function hijacks control keys causing remote desktop application not sending control keys

[Robin Hsu]

Reproduce steps:
1. launch a terminal
2. Type in 'gnome-tweak-tool' command
3. mouse click on "Keyboard and Mouse" -> "mouse: Show location of pointer" turning ON
4. close gnome-tweak-tool.
5. open Remmina Remote Desktop Client or VNC Viewer, and link to a remote windows machine.
  (On my machine, I launch vnc viewer as:
      /usr/lib/ssvnc/vncviewer -passwd .vnc/passwd 192.168.x.x)

6. Launch a notepad on the remote windows machine. Type something, use mouse drag-and-drop to select a word, and then type control-c (copy). It will just send 'c' rather than control-c. Thus you will see the whole word is replace by a single 'c'.

7. close remote connection. Turn "mouse: Show location of pointer" OFF, and do it again. This time, the copy action should work.

Note: The bug affects the control key. Thus control-c (copy) action is just one example. Other examples include control-x (cut), and control-v (paste).

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: gnome-tweak-tool 3.10.1-2ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-142.168~14.04.1-generic 4.4.167
Uname: Linux 4.4.0-142-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.29
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Mar 26 09:40:52 2019
InstallationDate: Installed on 2018-08-15 (222 days ago)
InstallationMedia: Ubuntu 14.04.5 LTS "Trusty Tahr" - Release amd64 (20160803)
PackageArchitecture: all
SourcePackage: gnome-tweak-tool
UpgradeStatus: No upgrade log present (probably fresh install)