Fix conversion of timestamps to (micro)seconds
Fix conversion of timestamps to (micro)seconds

Fix the externalization of timestamps to both microseconds and seconds
by properly convering the values to int64_t before performing any
operations on them.  This fixes the conversions under i386 as found
while running the Kyua test suite under Fedora's Koji.

rodrigc/kyua,rodrigc/kyua,jmmv/kyua,rodrigc/kyua,jmmv/kyua,rodrigc/kyua,jmmv/kyua,jmmv/kyua