hush: fix handling of backslashes in variable assignment

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/shell/hush_test/hush-vars/var_unbackslash.right b/shell/hush_test/hush-vars/var_unbackslash.right
new file mode 100644
index 0000000..20c2ddf
--- /dev/null
+++ b/shell/hush_test/hush-vars/var_unbackslash.right
@@ -0,0 +1,11 @@
+b1=-qwerty-t-\-"---z-*-?-
+b1=-qwerty-t-\-"---z-*-?-
+b2=-qwerty-\t-\-"-\--\z-\*-\?-
+b2=-qwerty-\t-\-"-\--\z-\*-\?-
+b3=-$a-\t-\\-\"-\--\z-\*-\?-
+b3=-$a-\t-\\-\"-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\--\z-\*-\?-
+Done: 0