RFC: init.sh: reject dash, due to its surprising local V='...' semantics

[Jim Meyering]

I was burned by dash's local V=' x' semantics, in spite of having
reported and studied this wart, at length, a few years ago. This arose
again when Assaf discovered one of grep's test programs would
malfunction on dash-based shells, e.g., on most Debian systems:
https://bugs.gnu.org/24116#11

I don't want to have to debug or think about this again -- at least
not in the free-software test scripts that I tend -- so propose to
make init.sh's initial shell-triage stage (where it tries to find a
useful shell, i.e., one that supports '$(...)', local and a few other
features) reject any shell like dash with this unfortunate and subtly
misleading attribute.

While currently dash cannot be said to be nonconforming, this
interpretation (thanks, Eric) suggests that the behavior of bash and
zsh is what will be standardized, so dash should change sooner rather
than later:

http://austingroupbugs.net/view.php?id=351

In the mean time, I feel more than justified in making our tests avoid dash.

If no one objects, I'll push this in a couple of days.

0001-tests-init.sh-exclude-dash-with-bad-local-semantics.diff
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