cast off_t as (unsigned long) so that tests build on MacOS 10.8. MacOS and FreeBSD should both serve as a useful reference for the correctness of the tests.

git-svn-id: svn://svn.code.sf.net/p/libkqueue/code/trunk@651 fb4e3144-bc1c-4b72-a658-5bcd248dd7f7