Fix value_type for numpy_expr

* value_type of : empty_like(ndarray<long, 2>) should be ndarray<long,1> instead of long
Add dtype and T attributes to numpy array
Fix shape for gslice

* case of gslice without all its dimension named in the slice
* ex: a.shape = (2,3,4)
    b = a[:,1]
    print b.shape
gslice are built from const array
Modification in indexed_array implementation
Improve gslice interface

* operator[]
* operator+=
* operator/=
* improve at performance
Fix islice

* avoid dangling reference (same issue than in imap b45f10ad2a28bd4fec027bd0a848304fb1d34663)
keep cpp files when compilation failed

* needed and really usefull for debug
export sliced string to python
Handle case of empty string
Add tests

* Many test from rosetta and for numpy
Fix assignment of gsliced_array
Merge pull request #128 from pbrunet/master

Improve numpy array + bugfixes

- Perf&features improvements for array slicing
- Handle case of empty string + sliced string export to python
- Indexed_array
- Add dtype and T attributes to numpy array
- Many tests from rosetta and for numpy