Bug #21143 Reorganizing of subpartitions let mysqld hang.

Description:
After the following ALTER statement mysqld and 11 threads hang:

ALTER TABLE systest1.tb6_eng1 REORGANIZE PARTITION part1,part2,part3,part4 INTO
(PARTITION part1 VALUES in(1,2,3,4) <data_directory> <index_directory>
(SUBPARTITION subpart11,SUBPARTITION subpart12,SUBPARTITION subpart13,SUBPARTITION subpart14,SUBPARTITION subpart15),
PARTITION part2 VALUES in (5,6,7,8) <data_directory> <index_directory>
(SUBPARTITION subpart21,SUBPARTITION subpart22,SUBPARTITION subpart23,SUBPARTITION subpart24,SUBPARTITION subpart25),
PARTITION part3 VALUES in (9,10,11,12) <data_directory> <index_directory>
(SUBPARTITION subpart31,SUBPARTITION subpart32,SUBPARTITION subpart33,SUBPARTITION subpart34,SUBPARTITION subpart35),
PARTITION part4 VALUES in (13,14,15,16) <data_directory> <index_directory>
(SUBPARTITION subpart41,SUBPARTITION subpart42,SUBPARTITION subpart43,SUBPARTITION subpart44,SUBPARTITION subpart45));

In the log file contains the following error message:
ERROR HY000: Can't create symlink './systest1/tb6_eng1#P#part2#SP#subpart22.MYI' pointing at '/data0/mysql/mysql-5.1/mysql-test/var/master-data/tmpindex/tb6_eng1#P#part2#SP#subpart22.MYI' (Error 17)

That there is a problem creating a symlink may be, but mysqld must not hang.

How to repeat:
follows as comment.

How to execute the attached program (test-21143.test):
perl mysql-test-run.pl --skip-ndb --suite experiments test-21143

To repeat the hangigng mysqld use "cre-alter-21143.sql" with mysql. Change the directories if necessary to those you want.

Reviewed by gluh

fixed in 5.1-kt tree

fixed in 5.1-kt team tree

Patch will appear in 5.1.12

Documented bugfix in 5.1.12 changelog.