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
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(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/strops3.tests b/shell/hush_test/hush-test2/strops3.tests
new file mode 100755
index 0000000..9274766
--- /dev/null
+++ b/shell/hush_test/hush-test2/strops3.tests
@@ -0,0 +1,13 @@
+# regex should accept '+' operator
+[[ abcdef =~ a[b-z]+ ]]; echo 1:YES:$?
+
+# newline matches by "match any" patterns
+v='
+'
+[[ "$v" =~ . ]]; echo 2:YES:$?
+[[ "$v" =~ "[$v]" ]]; echo 3:no:$? # hmm bash does return 1... why?
+[[ "$v" =~ [^a] ]]; echo 4:YES:$?
+# should work even without quotes:
+[[ $v =~ . ]]; echo 2u:YES:$?
+[[ $v =~ [$v] ]]; echo 3u:YES:$?
+[[ $v =~ [^a] ]]; echo 4u:YES:$?