`wptexturize()` adjustments:
* Only place an apostrophe before a number when it has exactly two digits.
* Never match '99' with the single prime pattern.
* Always assume '99' is an abbreviated year at the end of a quotation.
* Add unit tests.
* Resolves the unit test broken in [28721] for #8775.

See #26850.

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Add Unit Tests for i18n and `wptexturize()`. Don't confuse closing single quotes and apostrophes.

See #27426.

Built from https://develop.svn.wordpress.org/trunk@28762


git-svn-id: http://core.svn.wordpress.org/trunk@28575 1a063a9b-81f0-0310-95a4-ce76da25c4cd