Fix lock contention for HASHHDR.mutex

When Who What
2016-02-08 19:23:25 Álvaro Herrera (alvherre) Closed in commitfest 2016-01 with status: Returned with feedback
2016-01-27 15:26:14 Aleksander Alekseev (a.alekseev) New status: Ready for Committer
2016-01-22 10:56:38 Anastasia Lubennikova (lubennikovaav) Added lubennikovaav as reviewer
2015-12-11 14:11:55 Aleksander Alekseev (a.alekseev) Changed authors to Aleksander Alekseev (a.alekseev)
2015-12-11 14:11:31 Aleksander Alekseev (a.alekseev) Attached mail thread 20151211170001.78ded9d7@fujitsu
2015-12-11 14:11:30 Aleksander Alekseev (a.alekseev) Created patch record