Helper - NTP time adjustement for Wiz5100

[title]NTP time adjustement for Wiz5100[/title]
This is my version of NTPTime for use with the Wiznet5100 shield.
It is a corrected version of the one you can find elsewhere on this side or in the forums, and this one should be more robust.
It adjusts both system and RTC time, and accepts an offset in minutes, not hours (several countries uses an offset from GMT with half hours…).

Bug reports to f1iqf (at) hotmail (dot) com !