Fix pretty-printer test failure by carrying the bound lifetime names through

the types.  Initially I thought it would be necessary to thread this data
through not only the AST but the types themselves, but then I remembered that
the pretty printer only cares about the AST.  Regardless, I have elected to
leave the changes to the types intact since they will eventually be needed.  I
left a few FIXMEs where it didn't seem worth finishing up since the code wasn't
crucial yet.

src/libsyntax/ast.rs

@@ -904,6 +904,7 @@ pub struct TyClosure {
 pub struct TyBareFn {
     purity: purity,
     abi: Abi,
+    lifetimes: OptVec<Lifetime>,
     decl: fn_decl
 }