maintain and populate index automatically in background threads
update header
clean up tests
remove writer.deleteAll() in updateIndex()
update ApiTestBase and SchemaFactory to take serverManager() as arguments
add properties config in the server.properties file. call ex.store() adter appending the key
ex.store()
- adjust exchange to point at the first entry (both in addchange and addPopulate)
- getOperator() will do an ancestor_lookup_default IFF there is no branch_lookup_nested
clean up
remove unused code
fixup getChangedRows()
use next(boolean)
get populate-background-worker to work correctly.
remove formatting changes
- schedule a run for populate-worker upon starting up.

- nextInQueue() shouldn't do fetchAndRemove() because it is not guaranteed yet the index will be populated successfully.

- getChangeEntry() doesn't need to iterate over existing keys.
  (This is left-over code from the time when I wanted to remove entries with invalid indexId, but that seemed like an immature optimiation)
fix getOperator() as per the two comments. (hadn't really understood the diff between *_default and *_nested)
- record changes correctly in update/write_row
does not need to iterate over the keys
remove changes in conf/config/server.properties
- remove empty line from property file
- fix typo in property's name 
- fix getOperator(). The plan is computed in init() entirely based on the index's rowtype
- in persistitStore, add change-entry for the old row BEFORE it is deleted (both in UPDATE and DELETE)