CLONE -HSEARCH-189 : Thread management improvements for Master/Slave DirectoryProviders

http://opensource.atlassian.com/projects/hibernate/browse/HSEARCH-189

Concurrency problems when SharedReaderProvider opens a Reader can cause a later unit test to hang. This has been seen on linux 4 i386 and x86_64 platforms.

HSEARCH-189 mentions that part of the problem was fixed elsewhere.

Emmanuel or Hardy, do you know which other HSEARCH issues or revisions should also be backported?