Wrap valid_name in valid_ident for valid_feature_name
Wrap valid_name in valid_ident for valid_feature_name

I'm about to add another condition to whether a crate name is valid or
not that doesn't apply to feature names. Feature names really only want
to know if something is a valid identifier.

steveklabnik/crates.io,rust-lang/crates.io,steveklabnik/crates.io,rust-lang/crates.io,rust-lang/crates.io,steveklabnik/crates.io,steveklabnik/crates.io,rust-lang/crates.io