Tidy up retargeting code and debug.log output.
Tidy up retargeting code and debug.log output.

- remove unused int64_t retargetSpacing
- modulate timespan in an isolated int64_t nModulatedTimespan
- keep nActualTimespan intact, to retain the original value
- compress debug.log output from 5 into 3 lines while retaining
  all information.

brishtiteveja/sherlockcoin,jarymoth/dogecoin,jarymoth/dogecoin,coinwarp/dogecoin,langerhans/dogecoin,koharjidan/dogecoin,koharjidan/dogecoin,Exceltior/dogecoin,koharjidan/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,coinwarp/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,Exceltior/dogecoin,Domer85/dogecoin,Exceltior/dogecoin,coinkeeper/2015-06-22_18-37_dogecoin,koharjidan/dogecoin,marklai9999/Taiwancoin,brishtiteveja/sherlockcoin,coinkeeper/2015-06-22_18-37_dogecoin,Domer85/dogecoin,koharjidan/dogecoin,coinwarp/dogecoin,brishtiteveja/sherlockcoin,brishtiteveja/sherlockcoin,jarymoth/dogecoin,Exceltior/dogecoin,marklai9999/Taiwancoin,jarymoth/dogecoin,haisee/dogecoin,langerhans/dogecoin,coinwarp/dogecoin,marklai9999/Taiwancoin,langerhans/dogecoin,haisee/dogecoin,jarymoth/dogecoin,haisee/dogecoin,langerhans/dogecoin,langerhans/dogecoin,haisee/dogecoin,brishtiteveja/sherlockcoin,Domer85/dogecoin,marklai9999/Taiwancoin,koharjidan/dogecoin,langerhans/dogecoin,haisee/dogecoin,Domer85/dogecoin,Exceltior/dogecoin,coinwarp/dogecoin