Add "Require: timer" to 200 OK responses when appropriate.

The method by which the Require header is added to 200 responses is
inspired by the method that Olle Johansson uses in his darjeeling-prack
branch.

(closes issue ASTERISK-20570)
Reported by Matt Jordan, at the behest of Olle Johansson

Review: https://reviewboard.asterisk.org/r/2172
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Merged revisions 376521 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 376522 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@376550 65c4cc65-6c06-0410-ace0-fbb531ad65f3