MAPREDUCE-4892. Modify CombineFileInputFormat to not skew input slits' allocation on small clusters. Contributed by Bikas Saha.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1450912 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd
Merge remote branch 'origin/trunk-gd' into fb-Y-12345-trunk-gd