lib/sh/util.sh: log_custom(): use keyword-args syntax instead of local vars

lib/sh/util.sh: log_custom(): replace all non-whitespace chars in PS4 with $symbol instead of just the first one, so there aren't mixed $symbols and PS4 chars

lib/sh/util.sh: moved paths section after logging so it can use logging functions

*{.sh,run}: echo all global vars (except those defined before echo_vars is available)

web/links/index.htm.run: use the runscript-common $top_file, which is equivalent to $linked_file

*{.sh,run}: use new local_export instead of local...export. this still requires calling echo_vars manually, because local_export is an alias (and must be, to define the var in the caller's context).

lib/sh/util.sh: added local_export alias, which combines the effects of local and export

lib/sh/util.sh: renamed params() to kw_params() to clarify the type of params it handles

lib/sh/util.sh: logging: echo all keyword params by overriding params(). this requires removing manual echo_vars calls.

lib/sh/util.sh: moved functions section right after exceptions, so that other sections can use it. in particular, func_override is needed by verbose output to override non-verbose versions of functions.