Added disclaimer to WMS TileRetry feature - Development funded from Regione Toscana - SITA

as requested by Jürgen Fisher:

add discaliming with comments,
commented use of retry variable that could be avoided but leaved there to better readability 

main code merged with commits:
a563f2a650b13db9a1d7d58983ac2a2f5b87f1bb
3e278110f298bdf9363a936dd296b75b84858e6c