An explicit `cargo install ""` would cause clap to pass an empty crate-name,
leading to a panic(). We now assert() that Dependency::name is never the
empty string and prevent the situation in the first place by not allowing
the crate-name to be empty for `install`.
Fixes#5229
Previously we had logic to explicitly skip lock files but there's actually a
good case to read these from crates.io (#2263) so let's do so!
Closes#2263
Currently Cargo doesn't publish lock files in crates.io crates but we'll
eventually be doing so, so this changes Cargo to recognize `Cargo.lock` when
it's published to crates.io as use it as the basis for resolution during `cargo
install`.
cc #2263