hush: fix var_bash5.tests failure

function                                             old     new   delta
expand_one_var                                      1513    1552     +39
expand_pseudo_dquoted                                118     135     +17
expand_string_to_string                              110     126     +16
setup_heredoc                                        298     308     +10
expand_and_evaluate_arith                             69      79     +10
parse_stream_dquoted                                 233     241      +8
setup_redirects                                      220     225      +5
run_list                                             956     961      +5
expand_assignments                                    76      81      +5
run_pipe                                            1587    1590      +3
parse_stream                                        2371    2374      +3
builtin_umask                                        132     133      +1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 12/0 up/down: 122/0)            Total: 122 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

shell/hush_test/hush-vars/var_bash5.right

@@ -1,4 +1,11 @@
-a/
-a/d
-a/e/f
+1 a/
+2 a/d
+3 a/e/f
+4 a\
+5 a\d
+6 a\e\f
+7 a\\
+8 a\\d
+9 a\\e\\f
+a ab
 Done: 0

shell/hush_test/hush-vars/var_bash5.tests

@@ -4,8 +4,26 @@
 v='a/b/c'
 s='b/c'
 r='e/f'
-echo "${v/$s}"
-echo "${v/$s/d}"
-echo "${v/$s/$r}"
+echo "1 ${v/$s}"
+echo "2 ${v/$s/d}"
+echo "3 ${v/$s/$r}"
+
+v='a\b\c'
+s='b\\c'
+r='e\f'
+echo "4 ${v/$s}"
+echo "5 ${v/$s/d}"
+echo "6 ${v/$s/$r}"
+
+v='a\\b\\c'
+s='b\\\\c'
+r='e\\f'
+echo "7 ${v/$s}"
+echo "8 ${v/$s/d}"
+echo "9 ${v/$s/$r}"
+
+v='a-$a-\t-\\-\"-\`-\--\z-\*-\?-b'
+s='-$a-\\t-\\\\-\\"-\\`-\\--\\z-\\\*-\\\?-'
+echo "a ${v/$s}"
 
 echo Done: $?