Packages: systemd and other improvements.

See the following links for details:
https://github.com/nginx/unit/pull/212
https://github.com/nginx/unit/issues/213

Closes #155, closes #212, closes #213.

pkg/rpm/rpmbuild/SOURCES/unit.logrotate

@@ -0,0 +1,10 @@
+/var/log/unit/*.log {
+    missingok
+    nocreate
+    notifempty
+    postrotate
+        if [ -f /var/run/unit/unit.pid ]; then
+            /bin/kill -SIGUSR1 `cat /var/run/unit/unit.pid`
+        fi
+    endscript
+}