Review Board 1.7.22

MAPREDUCE-2584. Check for serializers early, and give out more information regarding missing serializers.

Review Request #885 - Created June 11, 2011 and submitted

Harsh J
As discussed on HADOOP-7328, MapReduce can handle serializers in a much better way in case of bad configuration, improper imports (Some odd Text class instead of the Writable Text set as key), etc..

This issue covers the MapReduce parts of the improvements (made to MapOutputBuffer and possible early-check of serializer availability pre-submit) that provide more information than just an NPE as is the current case.
Added a test case that expects a failure if no io.serializers are present.
Review request changed
Updated (June 16, 2011, 12:24 p.m.)
IOException catching ('stead of null).