Merge branch 'ps/dash-buggy-0.5.13-workaround'

The way dash 0.5.13 handles non-ASCII contents in here-doc is buggy and breaks our existing tests, which unfortunately have been rewritten to avoid triggering the bug. * ps/dash-buggy-0.5.13-workaround: t9300: work around partial read bug in Dash v0.5.13 t: work around multibyte bug in quoted heredocs with Dash v0.5.13