Coat

Hello, this is the patch I use to prevent delamination (cracks) when using ABS and full speed fan. The idea is to add a "coat" around the object during print. It isolates the walls from outside fresh air, and helps the object to cool down slowly.
The following picture shows the object printed
![idle_stand_habille](https://cloud.githubusercontent.com/assets/6553898/3555367/76d73aa4-0916-11e4-90b6-c75693538d86.jpeg)
And the following shows the object after having removed the "coat":
![idle_stand_nu](https://cloud.githubusercontent.com/assets/6553898/3555375/8d121fd2-0916-11e4-896e-00ce7529b88f.jpeg)
This pull request includes also the "stretch" modification and an extra outline around the raft to prime the extruder.