new format for continuous _changes feed

[Adam Kocoloski]

Hi folks, I was talking with aquarius and rnewson on IRC about a  
possible change to the format of the _changes feed.  We agreed that it  
made more sense for the feed=continuous mode to emit individual  
newline-delimited valid JSON Objects and skip the commas that are  
currently included.  This will allow consumers to split on newlines  
and immediately decode the result without any post-processing.   
feed=normal and feed=longpoll would stay unchanged.

If there are no objections I can make this change today and update the  
replicator as well.  Best,

Adam