wrong utcoffset for aware datetimes

[Alex Becker]

Calling utcoffset on a timezone using an aware datetime returns a different result than for a naive timezone. This makes datetime's isoformat() function return incorrect results.

import datetime
from pytz import timezone

tz = timezone('US/Pacific')
naive = datetime.datetime(2000,6,1)
aware = naive.replace(tzinfo=tz)

assert(tz.utcoffset(naive) == tz.utcoffset(aware))

The assertion fails. Note that this happens with every datetime/timezone combination I've tried, not just US/Pacific and 2000-06-01.