rustc: Fix formatting of env! error message

Death to caps.

Author: brson

src/libsyntax/ext/env.rs

@@ -43,7 +43,7 @@ pub fn expand_env(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
 
     let (var, _var_str_style) = expr_to_str(cx, exprs[0], "expected string literal");
     let msg = match exprs.len() {
-        1 => format!("Environment variable {} not defined", var).to_managed(),
+        1 => format!("environment variable `{}` not defined", var).to_managed(),
         2 => {
             let (s, _style) = expr_to_str(cx, exprs[1], "expected string literal");
             s

src/test/compile-fail/extenv-not-defined-default.rs

@@ -8,4 +8,4 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-fn main() { env!("__HOPEFULLY_NOT_DEFINED__"); } //~ ERROR: Environment variable __HOPEFULLY_NOT_DEFINED__ not defined
+fn main() { env!("__HOPEFULLY_NOT_DEFINED__"); } //~ ERROR: environment variable `__HOPEFULLY_NOT_DEFINED__` not defined