libmisc/copydir.c cleanup

libmisc/copydir.c cleanup
	* libmisc/copydir.c: Split copy_tree() in more maintainable functions:
	copy_entry(), copy_dir(), copy_symlink(), copy_hardlink(),
	copy_special(), and copy_file().
	* libmisc/copydir.c: -1 is used to indicate an error, directly set err
	to -1, instead of incrementing it, and checking if not nul at the
	end.