Windows: record history of read lock threads

Windows: record history of read lock threads

Maintance an array of up to 32 reader threads that have
acquired a rwlock.  Use it for debugging when things go bad.

Change-Id: I2e2e781ff355f1452e991898dfb5b91c47db9e34
Reviewed-on: http://gerrit.openafs.org/5411
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>