New Features

When closing the application it is showing "Closing..." screen now. It is necessary because closing can take some time until all threads (audio, video and network) are closed, especially if you are redirecting multiple USB devices.
A forced grab will disable client screen saver support and leave it to the host. When forcing a mouse grab with "Shift+F12", the client screen saver on the Linux machine will be disabled. It will be enabled again, once the force grab is released. This doesn't apply to a normal mouse grab, which is released with "Ctrl+Alt".
Removed confusing --no-relative option, grab works as follows. With enabled exclusive mouse grab, mouse is grabbed into window with first click. It will be indicated in the window title that mouse is grabbed and can be released via "Ctrl+Alt". If an application requests relative mouse mode, mouse is grabbed into window regardless if exclusive grab is enabled or disabled. It is necessary because some applications (mostly DirectX games) request relative pointer movements. In relative mouse grab the mouse cursor is hidden and it will be indicated in the window title that mouse is grabbed and can be released via "Ctrl+Alt". As soon as application releases relative grab, the previous mouse state is restored, either released or put back into exclusive grab mode.

Bug Fixes

Fixed unrecognized option (null) check
Fixed non-working USB redirection due to broken parameter check
Fixed compiler warning: too many arguments for format [-Wformat-extra-args]
Fixed #1 and it is possible to leave the window now regardless of mouse grab state