tests/auth.rs and tests/filters.rs contains the following path constant for running the binary in tests.

const SUCKIT: &'static str = "target/debug/suckit";

This seems to work with cargo test since it builds the binary in target/debug directory.
But in the cargo test --release case, those tests fail since the binary is located in target/release

This pull request removes the hardcoded path constant and uses the CARGO_BIN_EXE_<name> environment variable for finding the correct binary path. (See rust-lang/cargo#7697 for more information)