- particle drawing was using invalid memory with weights.

- particle set weight operator (Shift + K) and from the menu.
- mirror vertex groups operator can also flip weight group names.

a number of utility functions for weight groups added
 int *get_defgroup_flip_map(struct Object *ob);
 void flip_vertexgroup_name (char *name_r, const char *name, int strip_number); // moved from modifier.c 
 void copy_defvert (struct MDeformVert *dvert_r, const struct MDeformVert *dvert);
 void flip_defvert (struct MDeformVert *dvert, int *flip_map);

release/scripts/ui/space_view3d.py

@@ -186,6 +186,8 @@ class VIEW3D_MT_mirror(bpy.types.Menu):
             props.constraint_axis = (False, False, True)
             props.constraint_orientation = 'LOCAL'
 
+            layout.operator("object.vertex_group_mirror")
+
 
 class VIEW3D_MT_snap(bpy.types.Menu):
     bl_label = "Snap"
@@ -898,6 +900,7 @@ class VIEW3D_MT_particle(bpy.types.Menu):
             layout.operator("particle.subdivide")
 
         layout.operator("particle.rekey")
+        layout.operator("particle.weight_set")
 
         layout.separator()