PIPELINING_SERVER_BL: cleanup the internal list use

The list was freed incorrectly since the llist refactor of
cbae73e1dd. Added test 1550 to verify that it works and avoid future
regressions.

Reported-by: Pascal Terjan

Fixes #1584
Closes #1585

tests/data/Makefile.inc

@@ -165,6 +165,7 @@ test1520 test1521 \
 test1525 test1526 test1527 test1528 test1529 test1530 test1531 test1532 \
 test1533 test1534 test1535 test1536 test1537 test1538 \
 test1540 \
+test1550 \
 test1600 test1601 test1602 test1603 test1604 test1605 test1606 \
 \
 test1700 test1701 test1702 \

tests/data/test1550

@@ -0,0 +1,29 @@
+<testcase>
+<info>
+<keywords>
+multi
+</keywords>
+</info>
+
+# Server-side
+<reply>
+</reply>
+
+# Client-side
+<client>
+<server>
+none
+</server>
+# tool is what to use instead of 'curl'
+<tool>
+lib1550
+</tool>
+
+ <name>
+verify setting pipeling blacklisting options
+ </name>
+ <command>
+http://%HOSTIP:%HTTPPORT/1550
+</command>
+</client>
+</testcase>