Fix a bug in mod_expires. Previous to this patch, if you

Fix a bug in mod_expires.  Previous to this patch, if you
told mod_expires to add 604800 seconds to the last-modified
time, it actually added 604800 usec's to the last-modified time,
so that when looking at the response it looked like nothing
had been done.  The root of the problem was that we always compute
time in usec's, but we ask users to input sec's.  This means we
need to convert to usec's before using those values.
CS: Obtained from:

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@90066 13f79535-47bb-0310-9956-ffa450edef68