Check length of time format for ':' conditional in attime.py

This fixes https://github.com/graphite-project/graphite-web/issues/511 and allows you to use time format like '00:00' again.
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Merge pull request #522 from jssjr/alpha-sort-function

Add sortByName() function
Merge pull request #514 from tamale/master

Check length of time format for ':' conditional in attime.py