adding test case to check marking/unmarking

src/libsyntax/parse/token.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use ast;
-use ast::Name;
+use ast::{Name, Mrk};
 use ast_util;
 use parse::token;
 use util::interner::StrInterner;
@@ -557,6 +557,11 @@ pub fn fresh_name(src_name : &ast::Ident) -> Name {
     gensym(fmt!("%s_%u",ident_to_str(src_name),num))
 }
 
+// create a fresh mark.
+pub fn fresh_mark() -> Mrk {
+    gensym("mark")
+}
+
 /**
  * All the valid words that have meaning in the Rust language.
  *