If you type 'make distclean', this will destroy the generated makefiles,
and you need to run './configure' again before you can give any further
'make (all|install|clean|distclean|tgz|rpm|...)' command.
Now, this is quite annoying, so we've hacked the top-level makefiles so
that they do it automatically for you. If you type 'make xxx', the
top-level makefile will check that the generated makefiles (required to
perform the 'make xxx') exist. If they don't, it will automatically run
'./configure' for you to recreate them, then run 'make xxx' again.