Updated Linux joystick code to support hotplug, GUIDs, etc.

This uses libudev for hotplug, but it's optional, so we'll just try to find
 some reasonable defaults without it (maybe an older Linux box or under
 FreeBSD's Linux emulation?).

configure.in

@@ -1667,6 +1667,22 @@ CheckInputEvents()
         fi
 }
 
+dnl See if the platform offers libudev for device enumeration and hotplugging.
+CheckLibUDev()
+{
+    AC_ARG_ENABLE(libudev,
+AC_HELP_STRING([--enable-libudev], [enable libudev support [[default=yes]]]),
+                        , enable_libudev=yes)
+    if test x$enable_libudev = xyes; then
+        AC_CHECK_HEADER(libudev.h,
+                        have_libudev_h_hdr=yes,
+                        have_libudev_h_hdr=no)
+        if test x$have_libudev_h_hdr = xyes; then
+            AC_DEFINE(HAVE_LIBUDEV_H, 1, [ ])
+        fi
+    fi
+}
+
 dnl See if we can use the Touchscreen input library
 CheckTslib()
 {
@@ -2191,6 +2207,7 @@ case "$host" in
         CheckFusionSound
         CheckOpenGLX11
         CheckOpenGLESX11
+        CheckLibUDev
         CheckInputEvents
         CheckTslib
         CheckUSBHID