Merge r1664133, r1643284, r1621417 from trunk:

* Fix typo in error message

mpm_event(opt): zero is immutable.

Fix printf format spotted by cppcheck.
Untested.
Submitted by: rpluem, ylavic, jailletc36
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1678232 13f79535-47bb-0310-9956-ffa450edef68