lib/sh/util.sh: added plain()

inputs/XAL/Specimen/test.xml.ref: updated for sample data.csv, which contains the columns as a CSV. this fixes a bug where a map.csv must be used on a table that contains the same set of columns (ie. not one with no columns if there are any mappings).

bugfix: lib/sql_io.py: put_table(): is_literals: `return sql.value(cur): need to use sql.value_or_none() instead to support multi-row functions, such as _split() used in specimens data`

fix: inputs/input.Makefile: don't treat *.xml as data files since these are not currently supported

lib/runscripts/util.run: on_exit(): documented that users can also override gateway()/fallback() to perform other commands (or no commands) after the script is read

bugfix: lib/sh/db.sh: pg_table_exists(): need ! to negate boolean result

fix: lib/runscripts/table.run: table_make_install(): need to inform the user when it skips installing a table, because this is often unexpected

fix: lib/runscripts/util.run: run_args_cmd(): need to indent the output of the target that it's running

lib/runscripts/table.run: removed no longer used datasrc_make_install()

fix: lib/sh/util.sh: fade(): use medium gray instead of light gray because it fades on white and black backgrounds