Make datetime utils test runnable
Refactor test_iso2seconds to be more extendable
Improve iso2seconds test

- Add more test values.
- Correct assertTrue to assertEqual as it should be!
Add fractional duration to iso2seconds test
Add support for handling fractional seconds

- Add support for reading fractional seconds in 'aur', 'car' and 'star'
  records. The value is then rounded before being converted to an integer
  as the database only uses integers.
Allow use of ',' as decimal seperator in durations

- Allow use of ',' as decimal seperator in ISO 8601 durations.
- Add unit test for this case.
Update comments
Merge pull request #35 from apel/iss17-quick-fix

Add support for handling fractional seconds