Log Message:
Update shtk to 1.7:

**Released on 2017-02-17.**

* This is the first release with fixes for and confirmed to work with all
  of bash, dash, pdksh, and zsh.  We now have continuous integration runs
  for all these interpreters to ensure that this holds true in future
  releases.

* Added the `shtk_abort` function to terminate a script on fatal internal
  errors.

* Added the `shtk_cli_debug` function to log debug-level messages.

* Added the `shtk_cli_log_level` and `shtk_cli_set_log_level` functions to
  query and set the maximum log level.

* Added the `shtk_fs` module with the `shtk_fs_join_paths` and
  `shtk_fs_normalize_path` functions.

* Added the `shtk_hw` module with the `shtk_hw_ncpus` function.

* Fixed option parsing to detect missing arguments to options.

* Fixed pattern matching in `shtk_list_filter` so that it supports
  alternative branches.