Convert std::map::new_str_hash to istrs. Issue #855

src/comp/syntax/ast.rs

@@ -8,6 +8,8 @@ import codemap::filename;
 type spanned<T> = {node: T, span: span};
 
 type ident = str;
+type identistr = istr;
+
 // Functions may or may not have names.
 type fn_ident = option::t<ident>;