Optimization bugs fixed.
1. Add some missing properties for some expressions.
2. Add compute_shape() for expressions.
3. Turn on RotateSlice.
Merge branch 'master' into optimization
Add missing properties and functions to LocalWrapper
Add children_order parameters in Map and Reduce.
Iterate over children_order when order must be protected.
Comment
children is a ListExpr now
Merge branch 'optimization' into from_file_parallel

Conflicts:
	spartan/array/distarray.py
	spartan/expr/write_array.py
Remove redundant code