Expose fsync_fname as a public API.

Andres Freund
Keep heavily-contended fields in XLogCtlInsert on different cache lines.

Performance testing shows that if the insertpos_lck spinlock and the fields
that it protects are on the same cache line with other variables that are
frequently accessed, the false sharing can hurt performance a lot. Keep
them apart by adding some padding.
Remove dead URL mention in OSX startup script

Backpatch to 9.3.

Per suggestion from Gavan Schneider
Add GUC descriptions for compile-time postgresql.conf settings

Previous text was "No description available".

Tianyin Xu