feat(filterFilter): compare object with custom `toString()` to primitive

Closes #10464
Hm...these tests failed on some browsers (Chrome 39 on OS X). The failures are probably related to locale.
Changing `new Date(0)` to `new Date(1970, 0)` should fix the issue.

<sub>Alternatively, you could change `0` to `86400000` to ensure or timezones are in 1970, but I prefer the former approach.</sub>