changes to ediff-rcs-get-output-buffer

[Glenn Morris]

Michael Kifer wrote:

> * ediff-vers.el (ediff-rcs-get-output-buffer): make
> sure the buffer is created in fundamental mode.

This is a reversion of Stefan's change from 2009-08-28. The
let-binding of default-major-mode was removed because: i) that
variable is obsolete; and ii) it has no effect on the mode of the
buffer created by get-buffer-create (and never has had any). So
putting it back doesn't do anything.