reduce errors do not log to mapreduce_errors.log

With a new project, I created a map function that had emitted a set of integers with most items being processed, but in a few cases it would emit a value that was not an integer when the data didn't match the format.

The challenge is that I didn't know this until running over the production data set, and when the reduce failed to process the non-numeric info, it did not log to the mapreduce_errors.log. This made the issue hard to find. @vmx helped me find that the error was going to ns_server.couchdb.log:

[couchdb:error,2014-12-02T4:51:38.859,ns_1@ec2-54-160-64-77.compute-1.amazonaws.com
<ns_1@ec2-54-160-64-77.compute-1.amazonaws.com>:<0.21788.38>:couch_log:error:44]Uncaught
error in HTTP request: {throw,

{error, <<"Reducer: Error building index for view `s3counts`, reason: Value is not a number (key \"Xception-httpcode\")">>}

}