bugfix: inputs/input.Makefile: SVN: add: don't add subdirs for datasources marked _no_import (e.g. datasources which only have an inputs/ dir to be listed in VegPath)

bugfix: inputs/*/Source/data.csv for new-style datasources: need to include a blank row (plus a blank header) so that the metadata values are imported at least once instead of zero times, now that there is an installed staging table that will be iterated over. the blank row did not used to be necessary, because db_xml.put_table() has a special case for metadata-only tables with no installed table, which avoids iterating over the table's rows.

lib/sql_io.py: put_table() (column-based import): complexity note: clarified that INSERT RETURNING throws an error on duplicate instead of returning the existing row. added blank line after ¶ for readability.

lib/sql_io.py: put_table() (column-based import): warning about triggers populating unique constraint-covered columns: corrected limitation to include only the unique constraint used to do the DISTINCT ON, since other unique constraints are not affected by column-based import. note that the primary key will normally not be the DISTINCT ON constraint, so trigger-populated natural keys are supported unless the input table contains duplicate rows for some generated keys.

inputs/*/Source/ for new-style datasources: use an actual staging table instead of a metadata-only table, so that metadata values can be stored in the staging table instead of the map.csv (as will be required by new-style import)

inputs/input.Makefile: SVN: $(svnFilesGlob): added data.csv, used to store versioned data (such as the empty data.csv used by Source/ tables which have their metadata in the map table instead)

schemas/util.sql: type_qual(), type_qual_name(): added comments to distinguish these similarly-named functions, one of which gets a type qualifier and the other of which gets a qualified name (not the name of a type qualifier, which one might otherwise assume)

schemas/util.sql: typeof(): support expressions that are not relative to a table (which do not have a table_ param). note that this requires removing the STRICT qualifier, so that NULL expressions will now produce an error instead of passing through as NULL.

schemas/VegCore/VegCore.ERD.mwb: relationships legend: removed inheritance of base_class from record, so that the IS-A label would not confusingly appear to apply to the record connector stub instead of to the solid line between base_class and derived_class

bugfix: schemas/util.sql: col_names(): need to exclude dropped columns (which remain included in the pg_attribute table until the next tuple rewrite), by filtering on `NOT attisdropped`. lib/sql.py table_col_names() is not affected by this because it is able to access the column names from the DB driver directly, after performing `SELECT * FROM table LIMIT 0`.