in do_insertfile(), if we're in view mode, as we can be if multibuffer

in do_insertfile(), if we're in view mode, as we can be if multibuffer
mode is on, don't mark the file as modified (and remove the code that
does this in execute_command()); also, if we execute a command in a new
buffer, move back to the beginning of the first line of the buffer
afterwards, for consistency

git-svn-id: svn://svn.savannah.gnu.org/nano/trunk/nano@3785 35c25a1d-7b9e-4130-9fde-d3aeb78583b8