[PATCH] Fix memory leaks in auth_digest.cc

Hi all,
  the attached patch addresses Coverity issue 740431: in
Auth::Digest::Config::decode, username is allocated on the heap and
not freed in case of certain errors.

I've taken the chance to get rid of a few HEREs.

An alternate approach would be to pass Strings (eventually, SBufs)
around, so that the memory would be reclaimed automatically.

--
    /kinkie