lib/util.sh: exceptions: end_try* aliases: use new rethrow*

lib/util.sh: exceptions: added rethrow, rethrow_subshell aliases

lib/util.sh: always use '' rather than "" around alias definitions, to ensure that variables are evaluated at expand time rather than compile time

lib/util.sh: zip_newer/unzip_newer: evaluate $no_force at alias expansion time rather than at alias compile time, so that the $no_force can be overridden in the context the alias is used in

lib/util.sh: use `|| return` instead of `|| exit` because `|| exit` doesn't seem to work inside functions (it does not have the errexit effect). also, `|| return` has the advantage of not exiting the program if the caller used || after the command (i.e. as an error handler) to temporarily disable errexit.

lib/runscripts/util.run: tell users to override run_args_cmd rather than this function to perform other commands, so that on_exit () can contain other exit-related processing that should not be overriden by the user

lib/util.sh: removed "" around $?, $# because they are guaranteed to always be non-empty and contain no special chars

lib/util.sh: say "last space" instead of "trailing space" so the comment will be more likely to fit at the end of the line

lib/local.sh: removed mysql () since its functionality is now provided by mysql () in util.sh

lib/util.sh: mysql_cmd (): $server: like $ssh_server, clear the value when it's equal to this machine's hostname