Cleanup after [28671]:
* Set better defaults in `paginate_links()`, so that themes don't have to calculate them on their own, like Twenty Fourteen does now.
* Don't set page 1 to `?page=1` or `/page/1/` - that will force a canonical redirect.
* Add and cleanup unit tests

Props obenland, SergeyBiryukov, wonderboymusic.
Fixes #24606.


git-svn-id: https://develop.svn.wordpress.org/trunk@28785 602fd350-edb4-49c9-b593-d223f7449a82