bin/repl, lib/sql_gen.py Expression transforming: documented that this can also be done in Postgres with expression substitution (wiki.vegpath.org/Postgres_queries#expression-substitution)

bugfix: lib/runscripts/table.run: table_make_install(): need to ignore skip_table() errexit

lib/sh/util.sh: import_vars: documented that vars already set will not be overwritten

fix: lib/common.Makefile: $(nice): use an increment of +10 instead of +5 because +5 still leaves the shell sluggish

lib/common.Makefile: added $(nice) and use it everywhere its definition is used

fix: lib/sql_io.py: put_table(): don't warn if can't create pkey, because this just indicates that a set-returning function was used. this should get rid of the last of the confusing benign warnings in the test output.

fix: lib/sql.py: flatten(): don't warn if can't create pkey, because this just indicates that a set-returning function was used

lib/sql.py: run_query_into() added add_pkey_warn param to support turning off "could not create unique index" warnings, which are sometimes benign (eg. when using set-returning functions with column-based import)

lib/sh/util.sh: removed end_try_subshell, which now does the same thing as end_try

fix: lib/sh/archives.sh: unzip(): support -p option, which pipes extracted data to stdout