Add a match_ignore_ascii_case! macro that does not allocate.

It should replace `match foo.to_ascii_lower().as_slice() { ...}`

@Manishearth I changed map.get to map.find in the lint to work around an ICE:

    task 'rustc' panicked at 'couldn't find node id 0 in the AST map'

Does this look OK?

components/util/Cargo.toml

@@ -7,6 +7,9 @@ authors = ["The Servo Project Developers"]
 name = "util"
 path = "lib.rs"
 
+[dependencies.plugins]
+path = "../plugins"
+
 [dependencies.cssparser]
 git = "https://github.com/servo/rust-cssparser"
 

components/util/cursor.rs

@@ -19,8 +19,8 @@ macro_rules! define_cursor {
 
         impl Cursor {
             pub fn from_css_keyword(keyword: &str) -> Result<Cursor, ()> {
-                match keyword.to_ascii_lower().as_slice() {
-                    $( concat!($css) => Ok(Cursor::$variant), )+
+                match_ignore_ascii_case! { keyword:
+                    $( concat!($css) => Ok(Cursor::$variant) ),+
                     _ => Err(())
                 }
             }

components/util/lib.rs

@@ -31,10 +31,9 @@ extern crate string_cache;
 extern crate unicode;
 extern crate url;
 
-#[phase(plugin)]
-extern crate string_cache_macros;
-#[phase(plugin)]
-extern crate lazy_static;
+#[phase(plugin)] extern crate plugins;
+#[phase(plugin)] extern crate string_cache_macros;
+#[phase(plugin)] extern crate lazy_static;
 
 use std::sync::Arc;