Fixes ast_rwlock_timed[rd|wr]lock for BSD and variants.

The original implementations simply wrap pthread functions, which take
absolute time as an argument. The spinlock version for systems without
those functions treated the argument as a delta. This patch fixes the
spinlock version to be consistent with the pthread version.

(closes issue ASTERISK-20240)
Reported by: Egor Gorlin
Patches:
	lock.c.patch uploaded by Egor Gorlin (license 6416)
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Merged revisions 371718 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371720 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371721 65c4cc65-6c06-0410-ace0-fbb531ad65f3