This can prevent bizarre failures if, for example, you've done a
configuration in the top-level source directory, leaving behind one
config.h file, and then do an out-of-tree build in another directory,
with different configuration options. This way, we always pick up the
same config.h, in the build directory.
The purpose of this macro was to enable the file-by-file switch to NDO,
after which only tcpdump.c had a use of it and the definitions guarded
by it. Update tcpdump.c not to require them any more and dismiss the
unused definitions.
Remove lots of $Header's and a few $Id's that all belong to the former
CVS repository of tcpdump itself. These keywords have been frozen since
the migration to git in late 2008.
