Fixed ROOT dictionary generation for ROOT v6.02

Need to prefix header file names with "PACKAGE/" in DICTFWDDCLS
and DICTPAYLOAD.
Removed Props typedef from LinkDef

Typedef to inner class seems to break dictionary generation for
ROOT v6.02/00.
Using opaque pointer to hide internals of NameTable

* Workaround for problems with ROOT Cling and <mutex> header: Cling
  seems to have trouble including <mutex> on some platforms for some GCC
  configurations.

* Makes NameTable header very lightweight.
Removed unnecessary include of <memory> in Name.h