some copyright-notice problems in make 3.79.2a1

[Paul Eggert]

Many of the files in GNU make 3.79.2a1 have copyright notices that are
out of date.  For example, file.c was changed in 1998, 1999, 2000, and
2002, but the last year mentioned in the copyright notice is 1997.
Also, many of the files lack copyright notices.  acinclude.m4 is one
example.

<http://www.gnu.org/prep/maintain_8.html#SEC8> contains the gory
details about the form of copyright notices.