rust.inc: normalize to expanded 4 space tabs
rust.inc: normalize to expanded 4 space tabs

I had previously mixed using hard tabs, 8 spaces, and 4 spaces (due to
editor defaulting to hard tabs and the occasional change to 4 spaces to
work on python code).

Try to avoid that with a vim modeline

meta-rust/meta-rust,jmesmon/meta-rust,cardoe/meta-rust,cardoe/meta-rust,cardoe/meta-rust,jmesmon/meta-rust,meta-rust/meta-rust,jmesmon/meta-rust,starlab-io/meta-rust,meta-rust/meta-rust,jmesmon/meta-rust,cardoe/meta-rust,meta-rust/meta-rust,starlab-io/meta-rust,meta-rust/meta-rust