Prevent high resource usage when hashing large passwords. props mdawaffe, pento

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More tests for [30466]. props xknown.

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Twenty Fifteen: bring back the border between post navigation links we lost in the_post_navigation changes.

Props iamtakashi, fixes #30414.


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Correct an SQL syntax error introduced in r30158. Adds tests.

Fixes #30339
See #18962
Props julien731

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WordPress 4.1-beta2

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