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?

1 files changed, 3 insertions, 3 deletions

diff --git a/components/plugins/lints.rs b/components/plugins/lints.rs
index a170cb6a4a1..3cb4cb91e1f 100644
--- a/components/plugins/lints.rs
+++ b/components/plugins/lints.rs
@@ -104,8 +104,8 @@ fn lint_unrooted_ty(cx: &Context, ty: &ast::Ty, warning: &str) {
 // Determines if a block is in an unsafe context so that an unhelpful
 // lint can be aborted.
 fn unsafe_context(map: &ast_map::Map, id: ast::NodeId) -> bool {
-    match map.get(map.get_parent(id)) {
-        ast_map::NodeImplItem(itm) => {
+    match map.find(map.get_parent(id)) {
+        Some(ast_map::NodeImplItem(itm)) => {
             match *itm {
                 ast::MethodImplItem(ref meth) => match meth.node {
                     ast::MethDecl(_, _, _, _, style, _, _, _) => match style {
@@ -117,7 +117,7 @@ fn unsafe_context(map: &ast_map::Map, id: ast::NodeId) -> bool {
                 _ => false,
             }
         },
-        ast_map::NodeItem(itm) => {
+        Some(ast_map::NodeItem(itm)) => {
             match itm.node {
                 ast::ItemFn(_, style, _, _, _) => match style {
                     ast::UnsafeFn => true,