dot/emacs, dot/Xdefaults: Fix default frame width.

dot/emacs, dot/Xdefaults: Fix default frame width.

Two changes over the years.  Firstly, Emacs later than 21 (I think) have
fringes in which they display overflow markers, rather than needing a
text column for them, so we should set the default (one-column) frame
width to 77, rather than 78.  Secondly, I use very narrow fringes, so
Emacs's initial estimate of the frame width comes out wrong, so we need
to fiddle with the X resource.