This makes it much easier to determine what went wrong if an implementation
samples from the wrong location.

winex11: Remove set-but-never-read hwnd and fbconfig_id fields of struct x11drv_escape_set_drawable.

The swap interval is a property of the GLX drawable, which is destroyed and
recreated by set_gl_drawable_parent() and wglSetPixelFormatWINE().  When that
happens, copy the interval from the old gl_drawable and apply it at the next
call to wglSwapBuffers().

In its currrent implementation, cred_decode with input length 6 writes
6 bytes to the output buffer. This overflows the DWORD passed in
CredIsMarshaledCredentialW.