Change default time boundaries for raw queries

[jsternberg]

Changes the default time boundaries for raw queries so raw queries will
range until the end of time. Aggregate queries continue to have their
default end time be now().

Fixes #4461.

[jsternberg]

@rkuchan this change will need to be documented.

[beckettsean]

@jsternberg is my understanding correct?

SELECT * FROM foo           # will select until max(int64)-1
SELECT MEAN(*) FROM foo     # will select until now()
SELECT MAX(*) FROM foo      # will select until now()

[jsternberg]

I need to clarify the changelog since that's wrong. This is it:

SELECT * FROM foo                                   # will select until max(int64)-1
SELECT MEAN(*) FROM foo                             # will select until max(int64)-1
SELECT MAX(*) FROM foo                              # will select until max(int64)-1
SELECT MAX(*) FROM foo WHERE ... GROUP BY time(...) # will select until now()

[beckettsean]

Thanks for the clarification, @jsternberg.

The original comment has:Aggregate queries continue to have their default end time be now(), but if SELECT MEAN(*) FROM foo doesn't use now(), should that sentence in the comment be more like Queries with a group by time continue to have the default end time of now()?