Backtrace symbol demangler seems to be a bit broken

[sfackler]

This is what I get out of a backtrace on OSX with rustc 0.13.0-nightly (96a3c7c6a 2014-12-23 22:21:10 +0000):

error: internal compiler error: unexpected panic
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Tried to unwrap non-AST item: Bar', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/libregex/parse.rs:161

stack backtrace:
   1:        0x105ecfc38 - sys::backtrace::write::h329291c3ffa2342c0Jt
   2:        0x105ef0a03 - failure::on_fail::h17e4ace9633d727be0z
   3:        0x105e5cc3a - rt::unwind::begin_unwind_inner::h190be063817ae06eFHz
   4:        0x105e6115d - rt::unwind::begin_unwind_fmt::hc68ebd2b3de4118e2Ez
   5:        0x10467a318 - parse::Parser<$u{27}a$GT$::pop_ast::h7ee78731dd59df60vfb
   6:        0x10467142a - parse::Parser<$u{27}a$GT$::parse::hd65bf930804cbe0fk3a
   7:        0x10467c2ba - re::Regex::new::h23724d4cbd187d84ttc
   8:        0x10b689911 - native::h5a43b865124805f93aa
   9:        0x103653900 - ext::base::F.TTMacroExpander::expand::h1584431986571994
  10:        0x103f04dbb - ext::expand::expand_expr::unboxed_closure.55599
  11:        0x103f04392 - ext::expand::expand_expr::h97c236264ed38d26Rke
  12:        0x103eb9137 - ext::expand::MacroExpander<$u{27}a$C$$u{20}$u{27}b$GT$.Folder::fold_expr::h2f9526501e12f75dfof
  13:        0x103f13fd8 - ext::expand::expand_item_underscore::hbc130aa791daee70oMe
  14:        0x103f12532 - fold::noop_fold_item_simple::h10529280414042625464
  15:        0x103f12207 - ptr::P<T>::map::h14058766262738549160
  16:        0x103f0e3c8 - ext::expand::expand_item::he893952f6a05c984VEe
  17:        0x103f1afd4 - ext::expand::MacroExpander<$u{27}a$C$$u{20}$u{27}b$GT$.Folder::fold_item::h76a95980748c40b2Tof
  18:        0x103f1ada0 - fold::noop_fold_mod::unboxed_closure.55767
  19:        0x103f1ad19 - option::Option<T>::map::h11772459739700532410
  20:        0x103f1a8b6 - vec::Vec<T>.FromIterator<T>::from_iter::h652434281129776207
  21:        0x103f18c91 - fold::noop_fold_mod::h11818252818935706877
  22:        0x103f14412 - ext::expand::expand_item_underscore::hbc130aa791daee70oMe
  23:        0x103f12532 - fold::noop_fold_item_simple::h10529280414042625464
  24:        0x103f12207 - ptr::P<T>::map::h14058766262738549160
  25:        0x103f0df87 - ext::expand::expand_item::he893952f6a05c984VEe
  26:        0x103f1afd4 - ext::expand::MacroExpander<$u{27}a$C$$u{20}$u{27}b$GT$.Folder::fold_item::h76a95980748c40b2Tof
  27:        0x103f76917 - ext::expand::expand_crate::hfcbb6375468d5582qtf
  28:        0x10270cdcf - driver::phase_2_configure_and_expand::unboxed_closure.24614
  29:        0x1025f4e8f - driver::phase_2_configure_and_expand::hef0957bde6a7070cXha
  30:        0x1025e4527 - driver::compile_input::hdcb29128a43ec322wba
  31:        0x102785ff8 - thunk::Thunk<(*,$u{20}R$GT$::new::unboxed_closure.30336
  32:        0x102784038 - thunk::F.Invoke<A,$u{20}R$GT$::invoke::h12480167585331118411
  33:        0x1027827d9 - rt::unwind::try::try_fn::h9666833473335668351
  34:        0x105f58669 - rust_try_inner
  35:        0x105f58656 - rust_try
  36:        0x102782ed7 - thunk::F.Invoke<A,$u{20}R$GT$::invoke::h4838524648863172491
  37:        0x105edfc24 - sys::thread::thread_start::h7394d69fbc5b85e9vFw
  38:     0x7fff8cbb72fc - _pthread_body
  39:     0x7fff8cbb7279 - _pthread_body

Note the unexpanded $GT$s and $u{20} and $u{27}.

[sfackler]

cc @alexcrichton

[alexcrichton]

I think our list of what to demangle needs to be updated now that character escapes have changed as well.