(get_dest_mode): Rename from new_nondir_mode.

(get_dest_mode): Rename from new_nondir_mode.
Honor the umask for `cp', but not for `mv' or `cp -p'.
(copy_reg): New 4th parameter, dst_mode.  Pass it as 3rd arg. to open.
(copy_internal): Change type of locals `src_mode' and `src_type' from
int to mode_t.
Remove unnecessary local `fix_mode'.
Combine two if-stmts into one.
Pass `src_mode' as 4th arg to copy_reg.
If we've just created a new regular file, return early, skipping the
chmod step.  copy_reg now sets permissions of such files upon creation.
Use get_dest_mode, so there's just one chmod call here.