Data dependency: use fix-point on function's context

[montyly]

The data dependency uses a fix-point only at the contract's context, as a result, the function's context will miss some of the dependencies/taints

See: #156 (comment)

[montyly]

The issue is fixed in master.
We also added a new printer that should help to detect that kind of bug: data-dependency.

There is still room for improvements to the data dependency (ex: better support for self-dependency, or better support of structure and mapping), and we are going to continue to improve it's accuracy.

[cty12]

Seems to work now. Thanks!