Compatible 3.3+ (icalendar) and repaired format

Compatibility issue
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icalendar needs python 3.3+ or 2.6+ see <https://pypi.python.org/pypi/icalendar>
Default version in Ubuntu 12.04 (latest LTS) is python 3.2


Format
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I also repaired a format string
*Disclaimer* : I don't have python 3.3 installed, so I can't test this. Should be OK though.