These commits fix the test failures which were encountered in #948.
There's still the weirdness we discussed in the comments of #948 around different assertions being fired depending on the time zone of the machine, but I think that can be moved on to its own issue now.
cc @headius @BanzaiMan since I've chatted with both of you on this one.
Fix handling of Time offsets at DST boundaries.
Partly fixes #948
Fix handling of :dst Symbol in Time.new
Completely fixes #948