copyright notices on Info docs

[Dave Love]

[I thought I sent this, but I still have the draft.  Sorry if it's a
repeat.]

The Info version of the main manual doesn't show the actual copying
conditions as recommended in the Texinfo manual, and I think it
should.  It has the GFDL node, but no statement about invariant
sections or cover text.  The other Emacs manuals aren't consistent
about this (like other GNU manuals).

Perhaps standards.texi should stipulate using the Texinfo manual's
recipe.