Add missing ptype tag in glx.xml

Closes #22
diff --git a/xml/glx.xml b/xml/glx.xml
index 4ddd2f6..4ee1cae 100644
--- a/xml/glx.xml
+++ b/xml/glx.xml
@@ -1406,7 +1406,7 @@
         </command>
         <command>
             <proto><ptype>GLboolean</ptype> <name>glXSet3DfxModeMESA</name></proto>
-            <param>GLint <name>mode</name></param>
+            <param><ptype>GLint</ptype> <name>mode</name></param>
         </command>
         <command>
             <proto>void <name>glXSwapBuffers</name></proto>