V2.67: fix incorrect schedule date at the beginning of month

The date time conversion between UTC and local time may go wrong at the beginning of month. The “+1 month” may point to March, if you run it on 31th January (because 31th February doesn’t exist).

This version fixes this issue.

System time could go back to 1969 before sync with RTC

System time will go back to 1970 without RTC and fake-hwclock. By
having the timezone considered, it could actually go back to 1969.12.31.

V2.55

Software for Witty Pi 2, based on BASH.