fix: lib/sh/util.sh: stderr_matches(): usage: `rethrow` must be called right after stderr_matches(), to avoid calling running other commands if there is an error

fix: lib/sh/util.sh: stderr_matches(): when using $ignore_e, also set benign_error=1 to suppress the highlighting of the error

bugfix: lib/sh/db.sh: pg_schema_exists(): need to ignore benign error exit status from the "cannot create temporary relation in non-temporary schema" error

lib/sh/util.sh: stderr_matches(): supporting ignoring any benign error exit status associated with the error message being tested for

lib/sh/util.sh: stderr_matches(): usage: documented where any ignore_e statement would go

bugfix: lib/sh/util.sh: stderr_matches(): can't use `try` because this clears the exit status, which is needed for @PIPESTATUS to work. to support this, also need to avoid errexiting since @PIPESTATUS will be used instead.

lib/sh/util.sh: added dp(), which debug-prints a message

bugfix: inputs/VegBank/plot/postprocess.sql: use CVS.plot_ instead because that has the renamed staging table columns, and is compatible with auto-renaming of the SQL script columns

inputs/CVS/plot_/postprocess.sql: add unique constraint on locationName (analogous to the unique constraint in plot), for use by inputs/VegBank/plot/postprocess.sql in removing inter-datasource duplication

fix: schemas/util.sql: explain2notice_msg(): don't include EXPLAIN output for simple, single-value queries, to avoid cluttering up the log output