fix spelling in a comment

Backport of r739635 from trunk resp.
r1528780 from 1.5.x.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.4.x@1528782 13f79535-47bb-0310-9956-ffa450edef68
spelling fix

Backport of r1462813 from trunk resp.
r1462819 from 1.5.x.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.4.x@1528786 13f79535-47bb-0310-9956-ffa450edef68