bugfix: lib/runscripts/util.run: $subdirs: adjusted log_level now that echo_vars is one log_level lower

lib/runscripts/util.run: $wrap_fn: log at higher log_level because it's startup code

lib/sh/util.sh, runscripts/util.run: set_paths(): run with higher log_level to hide all the paths that are set at the beginning of the script

lib/runscripts/util.run: added sudo() override that uses $wrap_fn to support shell functions

fix: lib/runscripts/util.run: $wrap_fn: make it usable even if $top_script isn't world-executable

bugfix: lib/runscripts/import.run: all(): also need to propagate $rm to import()

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

added lib/runscripts/extract_header.run

fix: lib/runscripts/util.run: to_top_file(): handle $_remake properly, without requiring deferred_check_target_exists to set to_file()'s flags

*{.sh,run}: runscript targets: use begin_target instead of echo_func so the target name is properly echoed. note that this requires using with_rm so that $rm is properly progagated to applicable invoked targets. (previously, $rm was progagated to all invoked targets. note that with_rm only works inside a runscript target that starts with begin_target.)