(Finsert_file_contents): Run format-decode and

(Finsert_file_contents): Run format-decode and
after_insert_file_functions on entire buffer when REPLACE is
non-nil and inhibit modification_hooks and point_motion_hooks.
For consistency, run after_insert_file_functions iff something
got inserted.  Move signal_after_change and update_compositions
after code running after_insert_file_functions.  Make sure that
undo_list doesn't record intermediate steps of the decoding
process.