lib/sh/db.sh: pg_schema_exists(): documented that `try` is used to suppress the error exit status

lib/sh/util.sh: stderr_matches(): usage: surrounded command in if statement to indicate what context it would usually be used in

lib/runscripts/file.pg.sql.run, schema.pg.sql.run: support custom options to pg_dump in $@

lib/sql_io.py: automatic handling of input/output column type mismatches: also do this for identifying columns, which first cause an error in a join in sql.distinct_table() rather than in the main insert (and thus were not handled by the existing error handling). previously, the user would have had to manually cast the input column in postprocess.sql. this involves getting handle_MissingCastException() to update join_cols as well as mapping.

lib/sql.py: distinct_table(): don't cache the table creation, because this prevents different distinct_tables from being created for the same input table

lib/sql.py: create_table(), copy_table_struct(): support custom query options, such as cacheable

lib/sql_io.py: put_table(): main loop MissingCastException handler: factored out into nested function so that it can also be used elsewhere

lib/sql.py: parse_exception(): parse "operator does not exist" errors as MissingCastExceptions (these appear when a staging table column is of the wrong type)

fix: lib/Parser.py: syntax_err(): error message: lightened the shade of gray so the boundary between the strings before and after the error would be clearer

lib/runscripts/in_datasrc_dir.run: datasrc_make(): use `if remaking ...` instead of accessing $_remake manually, for clarity