Change "error" to "assert" to simplify code
Minor changes in implementation:

* Added two methods to make tranformation of data from [0,1] to/from [a,b] intervals more explicit:  rescale2_01 and rescale2_ab
* Minor changes to make implementation compatible with mex coder.
Buxfixes

1. validPhi was mispelled as ValidPhi when computing smolyak nodes
2. warning about node number adjusment was printed incorrectly