glx: Don't use 'new' as a function parameter name

Using 'new' as a function parameter name prevents including
glxclient.h the unit tests (future patch) that use the Google C++
Testing Framework.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
diff --git a/src/glx/glxclient.h b/src/glx/glxclient.h
index 13cd939..f8ae450 100644
--- a/src/glx/glxclient.h
+++ b/src/glx/glxclient.h
@@ -215,7 +215,7 @@
    void (*destroy)(struct glx_context *ctx);
    int (*bind)(struct glx_context *context, struct glx_context *old,
 	       GLXDrawable draw, GLXDrawable read);
-   void (*unbind)(struct glx_context *context, struct glx_context *new);
+   void (*unbind)(struct glx_context *context, struct glx_context *new_ctx);
    void (*wait_gl)(struct glx_context *ctx);
    void (*wait_x)(struct glx_context *ctx);
    void (*use_x_font)(struct glx_context *ctx,