Implementing Time#mktime

and some related methods while in the rabbit hole.
Fixing translation by bringing over helpers from PyPy
Untagging some more specs

and adding some comments around the time struct tuple.
Untagging more specs

and cleaning up the utils/time funcs to all return unwrapped values.
More translation-related fixes for Time methods
Minor change (reversal) to test to reduce diffstat
Cleaning up Time py tests
Not doing dumb stuff with ENV
Well, crud.  I'll get to this one in a follow-up.
Not using this anymore
Using correct monkeypatching method for TZ env var
Using now-available ENV.delete

thanks to #521
Backing out this bit as it isn't related to the Time stuff (anymore?)
Cleaning up Time#mktime/Time#local signature