convert_geonames_cities_to_textdb.py: New util to convert GeoNames city data to docs for cell salience name
Read salience from training data corpus if given
Make most_salient_document in GridDoc a string (doc's title)
Add Row object to textdb, redo read_textdb to use it
Use 'tail' instead of base etc. for last component of split path
io, hadoop: Various fixes for split_filename special cases
util.io: Add exists() to FileHandler
Make read_textdb take base not dir/prefix, allow dir or data/schema file also
Comment fixes
Implement --salience-file for id'ing cell by e.g. populous city