Resurrect BackwardSlice.
Resurrect BackwardSlice.

- Fill data into taint_graph. It might be renamed in the future though.
- Add proper sanity checks to some return values from other methods.
- Instead of getting all simple paths, now we only get shortest paths.
  Getting all simple paths is not feasible sometimes (especially when
  the program is big and loops exist).

iamahuman/angr,axt/angr,chubbymaggie/angr,axt/angr,tyb0807/angr,iamahuman/angr,axt/angr,tyb0807/angr,schieb/angr,chubbymaggie/angr,f-prettyland/angr,f-prettyland/angr,angr/angr,schieb/angr,f-prettyland/angr,chubbymaggie/angr,schieb/angr,angr/angr,tyb0807/angr,angr/angr,haylesr/angr,iamahuman/angr,haylesr/angr