Adopt commit b6d60d2 from master: Merge pull request #860 from jmendelsohn4/nb/bslma_readerwritermutex_20161115
Adopt commit b6d60d2 from master: Merge pull request #860 from jmendelsohn4/nb/bslma_readerwritermutex_20161115

commit b6d60d293b43e83620e64adb707905cc556b9896
Merge: 0a4c748 d2881e4
Author: Jeffrey Mendelsohn <JMENDELSOHN4@bloomberg.net>
Date:   Thu Nov 17 10:17:25 2016 -0500

    Merge pull request #860 from jmendelsohn4/nb/bslma_readerwritermutex_20161115

    added doc and lowered the threshold again

commit d2881e43865a734479bb517c897368c7846f13b7
Author: Jeffrey Mendelsohn <JMENDELSOHN4@bloomberg.net>
Date:   Thu Nov 17 10:16:07 2016 -0500

    added doc and lowered the threshold again

apaprocki/bde,bloomberg/bde,bloomberg/bde,dharesign/bde,bloomberg/bde,bloomberg/bde,bloomberg/bde,apaprocki/bde,che2/bde,che2/bde,dharesign/bde,dharesign/bde,apaprocki/bde,che2/bde,apaprocki/bde,dharesign/bde,che2/bde,apaprocki/bde