lib/tnrs.py: tnrs_request(): renamed to single_tnrs_request() to distinguish it from repeated_tnrs_request()

bin/tnrs_db: removed no longer used $wait flag (which caused tnrs_db to wait max_pause for new rows to be added), because tnrs_db is now invoked automatically after each import by the import_scrub target (in inputs/input.Makefile) and does not need to run as a daemon. note that when scrub is invoked, it is possible that a previous datasource's import has already scrubbed the names for this import, because tnrs_db runs until all rows in tnrs_input_name are scrubbed....

bin/tnrs_db: removed no longer needed explicit population of the Time_submitted, which is now done automatically by the tnrs table. however, this requires starting the transaction before submitting data, so Time_submitted is correctly set to the submission time rather than the insertion time. the setting of the correct time can be tested by inserting `time.sleep(n_sec)` after the TNRS request and checking that the Time_submitted is close to the time tnrs_db was run instead of n_sec seconds later.

bin/tnrs_db: start transaction before submitting data, so Time_submitted is correctly set to the submission time rather than the insertion time. these may differ by several minutes if TNRS is slow. the setting of the correct time can be tested by inserting `time.sleep(n_sec)` after the TNRS request, removing the explicit setting of Time_submitted, and checking that the Time_submitted is close to the time tnrs_db was run instead of n_sec seconds later.

bugfix: bin/tnrs_db: wrap just the TNRS request and the storing of the response data in a function (undoing part of r9514), because the transaction start time for Time_submitted should not be until the TNRS request is actually made (it often takes several minutes to materialize the next set of input names on a full DB)

bin/tnrs_db: Iterate over unscrubbed verbatim taxonlabels: put loop body in a function (which returns whether or not the loop should continue), so that the loop body can easily be wrapped in a transaction using sql.with_savepoint()

inputs/.TNRS/schema.sql: tnrs.Time_submitted: set default to now() (the timestamp of the start of the current transaction, http://www.postgresql.org/docs/9.1/static/functions-datetime.html) so that it would automatically be populated when rows are added. note that because the start of the current transaction instead of the exact time at insertion is used, all rows inserted in the same transaction (e.g. as part of the same batch) will have the same value for this, linking them together.

inputs/.TNRS/schema.sql: tnrs_populate_derived_fields(): renamed to tnrs_populate_fields() so it can be used to populate other fields as well

bin/tnrs_db: removed no longer needed explicit appending of derived cols, and instead use append_csv()'s new support for importing CSVs whose columns are a subset of the full table

bin/tnrs_db: ColInsertFilters: use the simpler literal value option for the mk_value param