Samba4 poor mans debug_ctx()

Samba4 poor mans debug_ctx()

DEBUG(), DEBUGADD() and friends can now use debug_ctx() in the
formatting expressions again,
e.g.

DEBUG(5,("Guid failed to match: %s\n", GUID_string(debug_ctx(), r->guid)));

Sadly it's done with macros (again) but when we need to save the 8 or 16
bytes of object code per DEBUG() expression we can do it the Samba 3 way
with added thread-safety for Samba 4. That could save up to 200K,
allowing 12 bytes for each occurrance of DEBUG...

Signed-off-by: Amin Azez <azez@ufomechanic.net>