The author lint was generating invalid code as shown on issue:
https://github.com/rust-lang-nursery/rust-clippy/issues/2442
I've changed the generated code to properly track cast
expressions.
Unfortunatelly, I've had to rewrite the `visit_decl` method, to
avoid that last if of the chain will be added. After looking at the code,
this last line was being added because of the `let x: char` part, but not
because of the `0x45df as char` expression.
It seems that let statements should not generate code on the author
lint, but I'm not sure that this is true or if I'm breaking
something on other code generation parts.
Finally, I've added a test for the author lint, but I'm not sure that
this needs to be added to the testsuite.
