Fix more extraction bits.
Fix more extraction bits.

- Implement a missing function in HyperHeap's FStar_ST.ml
- Implement a ST.get () for hyperheaps, even though extraction should not (?)
  generate references to this function.

YaccConstructor/FStar,MallabaevAzamat/FStar,A-Manning/FStar,YaccConstructor/FStar,FStarLang/FStar,FStarLang/FStar,FStarLang/FStar,YaccConstructor/FStar,A-Manning/FStar,YaccConstructor/FStar,MallabaevAzamat/FStar,hoheinzollern/FStar,MallabaevAzamat/FStar,A-Manning/FStar,hoheinzollern/FStar,MallabaevAzamat/FStar,hoheinzollern/FStar,hoheinzollern/FStar