Do not assume that days always have 86400 seconds

Make that date membership is computed correctly, even if a day has less
than 86400 seconds (e.g. after changing clocks).

Reported-by: Hakan Jerning <jerning@home.se>
Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

test/regress-001.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+
+. "${TEST_INIT:-./test-init.sh}"
+
+if [ "$1" = 'actual' ]; then
+  "$CALCURSE" --read-only -D "$DATA_DIR"/ -c "$DATA_DIR/apts-regress-001" \
+    -Q --filter-type=cal --from=2016-03-27 --days=2
+elif [ "$1" = 'expected' ]; then
+  cat <<EOD
+03/28/16:
+ * Day after clock adjustment
+EOD
+else
+  ./run-test "$0"
+fi