top: change man document license used from GFDL to GPL

top: change man document license used from GFDL to GPL

This patch brings the man document into agreement with
Debian's current licensing standards. The 3 urls below
discuss their concerns over the GFDL and also document
quite a few additional packages with similar licenses.

( jeeze, 12+ friggin' years & finally someone grep'd )
( for what was just a couple of 'invariant' sections )

Reference(s):
. why gfdl is unsuitable
http://www.debian.org/vote/2006/vote_001
. draft position statement
http://people.debian.org/~srivasta/Position_Statement.xhtml
. busted by lintian
http://lintian.debian.org/tags/license-problem-gfdl-invariants.html

Signed-off-by: Jim Warner <james.warner@comcast.net>