lib/sh/util.sh: cd(): always run cd with -P (expand symlinks) so that $PWD will contain a canonical path which matches the output of `readlink -f`. however, don't display the added -P in the logging output because it distracts from the directory being changed to.

lib/sh/util.sh: logging: added log+/-, which take a variable log_level step, and use them in log++/--

lib/sh/util.sh: repeat(): for simplicity and speed, just append to a local string var (and echo the result at the end) instead of using printf

bugfix: lib/sh/util.sh: repeat(): need to use %s instead of %q (escaped string) in printf

lib/sh/util.sh: logging: log++/--: comment about the different uses can be performed with one function: clarified that without a cmd, "$@" expands to nothing and assignments are applied to the caller

lib/sh/util.sh: log++/--: support running a command with the given log++/-- setting instead of applying it in the calling context. note that with no args, "$@" will expand to nothing and the var assignments will be applied in the calling context instead of to an executed command. this requires using $(()) syntax instead of let! to set the verbosity.

lib/sh/util.sh: logging: inlined PS4 functions into log++/-- because that's the only place they're used and it greatly simplifies the code

lib/sh/util.sh: log++/-- (and helpers PS4++/--): added functions for these so they can also be used in other contexts that don't support aliases. note that direct callers of the functions would still need to localize the PS4/$verbosity values using log_local.

lib/sh/util.sh: run_args_cmd(): moved test of $? to lib/runscripts/util.run on_exit() since it needs to be performed for all run_args_cmd() functions, not just the default implementation. (this test ensures that no commands are executed if the EXIT trap was encountered due to a parsing/loading error).

bugfix: lib/sh/util.sh: fwd(): need to use $top_dir (the runscript's file) instead of "${BASH_SOURCE¹}" (the caller's file)