The function relied on "List.map" which is not tail-rec. With enough
plevel, it provoked a stack overflow. I've simply fixed it by performing
the mapped computation inside the fold directly.

Uses a reference to a function provided by Eva to compute the dependency
of a term.

- Cabs2cil.is_boolean_result returns true if the expression is of type _Bool
- use standard result instead of custom expression for cast of a boolean to _Bool