Fix Latin spelling

"c.f." should be "cf.".

src/backend/replication/logical/origin.c

@@ -60,7 +60,7 @@
  *	 all our platforms, but it also simplifies memory ordering concerns
  *	 between the remote and local lsn. We use a lwlock instead of a spinlock
  *	 so it's less harmful to hold the lock over a WAL write
- *	 (c.f. AdvanceReplicationProgress).
+ *	 (cf. AdvanceReplicationProgress).
  *
  * ---------------------------------------------------------------------------
  */

src/backend/replication/logical/reorderbuffer.c

@@ -15,7 +15,7 @@
  *	  they are written to the WAL and is responsible to reassemble them into
  *	  toplevel transaction sized pieces. When a transaction is completely
  *	  reassembled - signalled by reading the transaction commit record - it
- *	  will then call the output plugin (c.f. ReorderBufferCommit()) with the
+ *	  will then call the output plugin (cf. ReorderBufferCommit()) with the
  *	  individual changes. The output plugins rely on snapshots built by
  *	  snapbuild.c which hands them to us.
  *
@@ -1752,7 +1752,7 @@ ReorderBufferForget(ReorderBuffer *rb, TransactionId xid, XLogRecPtr lsn)
 /*
  * Execute invalidations happening outside the context of a decoded
  * transaction. That currently happens either for xid-less commits
- * (c.f. RecordTransactionCommit()) or for invalidations in uninteresting
+ * (cf. RecordTransactionCommit()) or for invalidations in uninteresting
  * transactions (via ReorderBufferForget()).
  */
 void

src/backend/replication/logical/snapbuild.c

@@ -42,7 +42,7 @@
  * catalog in a transaction. During normal operation this is achieved by using
  * CommandIds/cmin/cmax. The problem with that however is that for space
  * efficiency reasons only one value of that is stored
- * (c.f. combocid.c). Since ComboCids are only available in memory we log
+ * (cf. combocid.c). Since ComboCids are only available in memory we log
  * additional information which allows us to get the original (cmin, cmax)
  * pair during visibility checks. Check the reorderbuffer.c's comment above
  * ResolveCminCmaxDuringDecoding() for details.