GlobalShortcut_unix: request latest XInput 2 version by default.

Previously, Mumble used to explicitly request XInput 2.0.

However, if apps such as Chrome (that use XInput 2.2, if possible)
were in the foreground, we would not properly receive raw release
events for mouse buttons.

Using the latest version (or, at least 2.2), seems to solve
the problem.

Fixes #1319

src/mumble/GlobalShortcut_unix.cpp

@@ -91,8 +91,8 @@ GlobalShortcutX::GlobalShortcutX() {
 	int evt, error;
 
 	if (g.s.bEnableXInput2 && XQueryExtension(display, "XInputExtension", &iXIopcode, &evt, &error)) {
-		int major = 2;
-		int minor = 0;
+		int major = XI_2_Major;
+		int minor = XI_2_Minor;
 		int rc = XIQueryVersion(display, &major, &minor);
 		if (rc != BadRequest) {
 			qWarning("GlobalShortcutX: Using XI2 %d.%d", major, minor);

src/mumble/GlobalShortcut_unix.h

@@ -38,6 +38,7 @@
 #include <X11/X.h>
 #include <X11/Xlib.h>
 #ifndef NO_XINPUT2
+#include <X11/extensions/XI2.h>
 #include <X11/extensions/XInput2.h>
 #endif
 #include <X11/Xutil.h>