1) Adjust IndexMerger to create convert the indexes it creates from the old format to the new.  This is done quite sub-optimally, but it will work for now...
Merge branch 'master' of github.com:metamx/druid
1) Remove vast majority of usages of IndexIO.mapDir() and deprecated it.  IndexIO.loadIndex() is the new IndexIO.mapDir()
2) Fix bug with IndexMerger and null columns
3) Add QueryableIndexIndexableAdapter so that QueryableIndexes can be merged
4) Adjust twitter example to have multiple values for each hash tag
5) Adjusted GroupByQueryEngine to just drop dimensions that don't exist instead of throwing an NPE