Remove mpool_tree_item from the mpool_tree before unregistering/freeing memory.

Otherwise a race exists if another thread allocates already freed memory
which is not removed from the mpool_tree yet.

This commit was SVN r16038.

ompi/mca/mpool/base/mpool_base_alloc.c

@@ -290,8 +290,9 @@ int mca_mpool_base_free(void *base)
         return OMPI_SUCCESS;
     }
 
-    unregister_tree_item(mpool_tree_item);
     rc = mca_mpool_base_tree_delete(mpool_tree_item);
+    if(OMPI_SUCCESS == rc)
+        unregister_tree_item(mpool_tree_item);
     
     return rc;
 }