Several my own fixes/cleanups:
- make it use mkstemp() instead of less secupe mktemp();
- HAS_CONFIGURE --> GNU_CONFIGURE;
- install README into separate bulk_mailer directory under ${PREFIX}/share/doc,
not just ${PREFIX}/share/doc/bulk_mailer.README.
PR: 19100
Submitted by: Ying-Chieh Liao <ijliao@Terry.Dorm8.NCTU.edu.tw>