Add pkgid attribute.
Stop using rustpkg for building and use make instead.

rustpkg still seems to have some issues, most significantly it can't handle
the rust-crypto-util crate all that well - doing a rustpkg install to fetch
this project results in an error trying to build rust-crypto-util.
Rename rust-crypto-util's main.rs to tool.rs

Doing this renaming prevents rustpkg from trying to compile the tool. This
works around a bug in rustpkg install that causes errors when using rustpkg
to fetch this project from a remote location.