Fca/fix findroot

This is for review, we cannot merge yet because it does not work with the current version of ROOT due to a problem in ROOT compiler option definition. When the ROOT team provides us with a tag with the necessary fix, we will install it on afs and we will consider the merge. All users will have then to install the new version of root.

27-6-16 The new version of root should be there. Depending on the result of the test we can merge.