Prevent adding a bundle prefix when creating a term.

#6196 

In this PR we prevent the addition of the bundle prefix when a term is saved (to avoid a source of the form ``blog/taxonomy/term/1``).

Creating a vocabulary associated with the bundle "blog":
![selection_226](https://cloud.githubusercontent.com/assets/4497748/3144991/57ed4224-ea2f-11e3-98c8-d1d003489a0c.png)

Adding a term:
![selection_227](https://cloud.githubusercontent.com/assets/4497748/3144993/57efb216-ea2f-11e3-80d5-abd8c68674b5.png)

The link for the term is now fixed:
![selection_228](https://cloud.githubusercontent.com/assets/4497748/3144992/57ef12fc-ea2f-11e3-939c-07cdee1f2464.png)