Atomic ops for unlogged LSN

[John Morris]

This is a short patch which cleans up code for unlogged LSNs. It replaces the 
existing spinlock with
atomic ops.  It could provide a performance benefit for future uses of
unlogged LSNS,  but for now it is simply a cleaner implementation.

0001-Use-atomic-ops-for-unloggedLSNs.patch
Description: 0001-Use-atomic-ops-for-unloggedLSNs.patch