Vim: Stop highlighting foo in `use foo;` specially

This wasn’t really consistent with other things; the last section of the
import was not highlighted in any other case.

Also `use {foo, bar};` was having the foo and bar not highlighted, where
they would have been as separate statements.
Highlight `extern crate "foo" as bar;` properly.
Highlight 1..2 according to the current grammar.
auto merge of #18023 : chris-morgan/rust/vim-misc-2014-10-14, r=kballard

- Stop highlighting foo in `use foo;` specially.
- Highlight `extern crate "foo" as bar;` properly.
- Highlight 1..2 according to the current grammar.