Merge r238637,r238640,r238641,r238642:

Merge r238637,r238640,r238641,r238642:

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r238637 | davidxu | 2012-07-20 09:56:14 +0800 (Fri, 20 Jul 2012) | 6 lines

Don't forget to release a thread reference count,
replace _thr_ref_add() with _thr_find_thread(),
so reference count is no longer needed.

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r238640 | davidxu | 2012-07-20 11:00:41 +0800 (Fri, 20 Jul 2012) | 2 lines

Eliminate duplicated code.

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r238641 | davidxu | 2012-07-20 11:16:52 +0800 (Fri, 20 Jul 2012) | 2 lines

Eliminate duplicated code.

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r238642 | davidxu | 2012-07-20 11:22:17 +0800 (Fri, 20 Jul 2012) | 2 lines

Don't assign same value.

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/9@238714 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f