V-Slot - OpenBuilds Printable Corners

While building [Ultimaker 2 Aluminum Extrusion](http://www.thingiverse.com/thing:811271).
I decided to replace corner brackets with single pice corner part. It suppose to raise frame rigidity and simplify assembly process.
These parts are designed mainly for [V-Slot from OpenBuilds](http://openbuildspartstore.com/v-slot/?sort=bestselling).
Thus may **not work** with other extrusion shape.
Besides they are perfectly printable - almost no support needed.

*Please pay attention that bott