Use difftime() to subtract time_t values.

ChangeLog

+2001-10-26  Per Cederqvist  <ceder@moria>
+
+	Use difftime() to subtract time_t values.
+	* src/server/rfc931.c (get_real_username): Use difftime() instead
+	of '-'.  (Bug 103).
+	* src/server/dbck-cache.c (timerdiff): The tv_usec part of the
+	timeval is ignore.  Added a comment documenting that that is OK.
+
 2001-10-04  Per Cederqvist  <ceder@moria>
 
 	* TODO (BUGZILLA-MARKER): Start to move stuff to