Eliminate -Wshadow warnings

actually changed 3 files, but I see more files here, I think I am being beaten around by git ?
these are the changed files, hopefully you can see a difference : 

Foundation/include/Poco/Timespan.h
Net/include/Poco/Net/ICMPEventArgs.h
Net/include/Poco/Net/SocketAddress.h

PS : help on how to get my git checkout up to date is welcome, git seems difficult :-(