Clear up the last of the Doxygen warnings

Clear up the last of the Doxygen warnings

base/statistics.hh:
    Document the friend class because doxygen can't handle the template instantiation.
kern/tru64/dump_mbuf.cc:
kern/tru64/dump_mbuf.hh:
kern/tru64/printf.cc:
kern/tru64/printf.hh:
kern/tru64/tru64_events.cc:
    Change namespace from Tru64 to tru64 (There is a class Tru64, and it was confusing doxygen).

--HG--
extra : convert_revision : 9644b1324814952cb6a2d98fd2ab4d07f0860b45