adding graphite/webapp/graphite/readers subdir.
mongodb finder improvments.
split readers.py into separate files in a readers directory so can add a mongodb reader.  Fixed imports so handle new location.
fixed finders so can find readers.  added mongodbReader.
fixed finders so can find readers.  added mongodbReader.
fixed finders so can find readers.  added mongodbReader.
adding metricValuePool.
adding test_mongoReader.py
moving metricValuePool back to backends/mongo/.
adding scripts to doMongoInit.
adding scripts to doMongoInit.
adding tests subdir to backends/mongodb.
fixing up metricType and metricValue imports, adding dataNormalizer.
same as previous commit.
many updates, can get branches of tree now, not leaves though.
many updates, can get branches of tree now, not leaves though.
modified files, fixed some problems.
had to modify node.py so it can defer requests to get data until we actually need it; otherwise prefetches lots of needless stuff.