shell: better support of [[ ]] bashism

Still rather rudimentary for ash

function                                             old     new   delta
binop                                                433     589    +156
check_operator                                        65     101     +36
done_word                                            736     769     +33
test_main                                            405     418     +13
parse_stream                                        2227    2238     +11
ops_texts                                            124     133      +9
ops_table                                             80      86      +6
run_pipe                                            1557    1562      +5
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 8/0 up/down: 269/0)             Total: 269 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/hush_test/hush-test2/strops2.right b/shell/hush_test/hush-test2/strops2.right
new file mode 100644
index 0000000..8ddb4b0
--- /dev/null
+++ b/shell/hush_test/hush-test2/strops2.right
@@ -0,0 +1,6 @@
+1:ERR2:2
+2:YES:0
+3:YES:0
+4:YES:0
+5:no:1
+6:YES:0