Commit message:
devel/shell-toolbox: Update to 20180719 Changelog: * A skeleton directory (to pre-populate the temporary working directory with) may be specified by setting the SHELL_SKEL environment variable to the path of a directory. This environment variable is not used if the command line option -s or -d is used. * /bin/sh is used if SHELL is empty or unset and no other shell is specified.