The fix for 6633275 (translucent and shaped windows) introduces use of the XRENDER
extension in awt_GraphicsEnv.c After loading the library, the code starts making
calls, but doesn't first check if the extension is in fact supported.

On at least some versions of Xlib this is obvious because you get a ton of messages :
Xlib: extension "RENDER" missing on display "myhost:0.0"
Xlib: extension "RENDER" missing on display "myhost:0.0".
Xlib: extension "RENDER" missing on display "myhost:0.0".
....