redo-sh: downgrade failures that affected dash; add a bash warning.

I feel a little dirty doing this, but the way the code was before, redo
almost always picked bash as the shell.  bash is way too overpowered
and this led to bashisms in do scripts unnecessarily.  The two failures
in dash are things that I would really like to have, but they haven't
materialized after 6 years, so I guess we should be realistic.

To appropriately penalize bash for asking for trouble, I added a
warning about [ 1 == 1 ] syntax being valid (as opposed to the POSIX
correct [ 1 = 1 ]).  This allows dash to be selected ahead of bash.

I also moved 'sh' to the end of the list, because although it's the
weakest shell on some systems, on other systems it's just bash.  And I
put zsh in front of bash, because fewer people have zsh and we want
them to test zsh.

t/dotparams.od

@@ -1,2 +1,2 @@
 # call this as ". ./dotparams.od a b" from shelltest.od
-[ "$1" = a ] && [ "$2" = b ] && [ "$#" = 2 ] || fail 115
+[ "$1" = a ] && [ "$2" = b ] && [ "$#" = 2 ] || warn 115