LoggerAPI: present the timestamp key as a string
LoggerAPI: present the timestamp key as a string

This imitates what the old code did; lots of stuff upstream
depends on this behavior.

kgjamieson/NEXT,nextml/NEXT,kgjamieson/NEXT,nextml/NEXT,kgjamieson/NEXT,nextml/NEXT,nextml/NEXT,kgjamieson/NEXT