Depending on certain conditions it was possible for the hashtab counting thread
to starve other threads, preventing them from executing in the expected fashion.
This change adds a sleep to allow the others to do what they need to do. While
this doesn't thrash the hashtab as much as previously, it at least works.

(closes issue ASTERISK-22276)
Reported by: Matt Jordan
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Merged revisions 396619 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 396620 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@396621 65c4cc65-6c06-0410-ace0-fbb531ad65f3