input.Makefile: Staging tables installation: %/install: Also create header.csv so that there is a CSV header that the map spreadsheets can be autogenerated from

input.Makefile: Staging tables installation: %/install: Add row_num column to derived staging tables so they will have a pkey

sql.py: pkey(): Use pkey_col constant if this column exists, to allow using a row_num column as the pkey even when it is placed at the end of the table (due to being added after the table was created)

input.Makefile: Staging tables installation: %/install: Support alternative generation of a staging table by joining together other staging tables in a create.sql file

input.Makefile: Staging tables installation: %/install: Don't create a row_num column when the table is a joined table because it collides during joins

csv2db: Made input_cmd optional when errors_table_only is on, because the CSV header is not needed to create the errors table

csv2db: Added has_row_num param to disable creating a row_num column

input.Makefile: Existing maps discovery: $(allTables): When prepending unsorted (joined) tables, save them in $(joinedTables) for later use in determining which tables should have a row_num column

README.TXT: Fixed indent

input.Makefile: Staging tables installation: Install all tables, not just those present in import_order.txt. This will later allow staging tables to be derived by joining together other staging tables, which themselves are not imported but still need to be installed.