tzstr not properly detecting invalid strings

[pganssle]

I noticed that this test is not actually parsing the time zone string correctly because that string format is not supported:

>>> from dateutil import tz
>>> tz.tzstr("EST5EDT") == tz.tzstr("EST5EDT,4,1,0,7200,10,-1,0,7200,3600")
True
>>> tz.tzstr("EST5EDT") == tz.tzstr("EST5EDT,5,4,0,7200,11,-3,0,7200,3600")
True

I'm thinking maybe once this is fixed, these tests should be switched to compare tzstr to tzrange, or to some performance-based tests (like checking that the transitions happen at the right time, etc.

[pganssle]

Putting this off for the first bugfix release.