file operations like Append/Prepend that are specific to the "Write
File" prompt, and change the Mac format toggle to Meta-M, since that no
longer conflicts with the mouse support toggle; update the documentation
accordingly


git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@2023 35c25a1d-7b9e-4130-9fde-d3aeb78583b8