1.2.x, %f.1 seconds --> %.1f seconds and a comment in mod_cproxy_cluster...


 * %f.1 seconds --> %.1f seconds in ModClusterLogger.java
 * removed unused variables in mod_proxy_cluster.c
 * Added a hint for anybody who tries anything like ```ProxyPass / balancer://supercluster``` while having the default ```ManagerBalancerName mycluster```.