Also, do more error checking on the arguments specified to the REALTIME()
function and clarify the documentation.  While I was editing the file, a
few coding guidelines fixups, as well.

Review: https://reviewboard.asterisk.org/r/2031/
........

Merged revisions 369937 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 369938 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@369940 65c4cc65-6c06-0410-ace0-fbb531ad65f3