Otherwise, it may be possible for the user running sudoedit to
replace the newly-created temporary files with a symbolic link and
have sudoedit set the owner of an arbitrary file.
Problem reported by Matthias Gerstner of SUSE.
Previously we needed to include headers required by the various
sudo*h files. Now those files are more self-sufficient and we
should only include headers needed by code in the various .c files.
