shell: tweak bkslash_in_varexp.tests, add bkslash_in_varexp1.tests

It turns out bkslash_in_varexp.tests was a bash bug :]

ash and hush fail "corrected" bkslash_in_varexp.tests as well,
just not as badly as I thought (hush gets half of the cases right).

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/hush_test/hush-quoting/bkslash_in_varexp.tests

@@ -1,4 +1,14 @@
-x=a
+x='a]'
+#
+# \] is not a valid escape for ] in set glob expression.
+# Glob sets have no escaping at all:
+# ] can be in a set if it is the first char: []abc],
+# dash can be in a set if it is first or last: [abc-],
+# [ and \ need no protections at all: [a[b\c] is a valid set of 5 chars.
+#
+# bash-4.3.43 misinterprets [a\]] as "set of 'a' or ']'".
+# Correct interpretation is "set of 'a' or '\', followed by ']'".
+#
 echo Nothing:${x#[a\]]}
 echo Nothing:"${x#[a\]]}"
 echo Nothing:${x%[a\]]}

shell/hush_test/hush-quoting/bkslash_in_varexp1.right

@@ -0,0 +1,5 @@
+Nothing:
+Nothing:
+Nothing:
+Nothing:
+Ok:0

shell/hush_test/hush-quoting/bkslash_in_varexp1.tests

@@ -0,0 +1,6 @@
+x=a
+echo Nothing:${x#[]a]}
+echo Nothing:"${x#[]a]}"
+echo Nothing:${x%[]a]}
+echo Nothing:"${x%[]a]}"
+echo Ok:$?