test, provide regression for shell option
hygiene, free cmd'ified shell command upon fini_chld()
minor, allow shell to be set on a per-test basis using `setopt shell ...'
minor, redo the option setting work-flow
hygiene, also free strndup()'d shell commands
test, fix, avoid SIGCHLDs when using /bin/true
Merge branch 'feat/shell'

* feat/shell:
  test, fix, avoid SIGCHLDs when using /bin/true
  hygiene, also free strndup()'d shell commands
  minor, redo the option setting work-flow
  minor, allow shell to be set on a per-test basis using `setopt shell ...'
  hygiene, free cmd'ified shell command upon fini_chld()
  test, provide regression for shell option