Remove duplicated words split across lines in comments

This has been detected using some interesting tricks with sed, and the
method used is mentioned in details in the discussion below.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20180908013109.GB15350@telsasoft.com

src/backend/access/gin/ginbtree.c

@@ -211,7 +211,7 @@ freeGinBtreeStack(GinBtreeStack *stack)
 /*
  * Try to find parent for current stack position. Returns correct parent and
  * child's offset in stack->parent. The root page is never released, to
- * to prevent conflict with vacuum process.
+ * prevent conflict with vacuum process.
  */
 static void
 ginFindParents(GinBtree btree, GinBtreeStack *stack)

src/backend/access/transam/twophase.c

@@ -1726,7 +1726,7 @@ RecreateTwoPhaseFile(TransactionId xid, void *content, int len)
  * possible that GXACTs that were valid at checkpoint start will no longer
  * exist if we wait a little bit. With typical checkpoint settings this
  * will be about 3 minutes for an online checkpoint, so as a result we
- * we expect that there will be no GXACTs that need to be copied to disk.
+ * expect that there will be no GXACTs that need to be copied to disk.
  *
  * If a GXACT remains valid across multiple checkpoints, it will already
  * be on disk so we don't bother to repeat that write.

src/backend/access/transam/xlogarchive.c

@@ -422,7 +422,7 @@ ExecuteRecoveryCommand(const char *command, const char *commandName, bool failOn
 /*
  * A file was restored from the archive under a temporary filename (path),
  * and now we want to keep it. Rename it under the permanent filename in
- * in pg_wal (xlogfname), replacing any existing file with the same name.
+ * pg_wal (xlogfname), replacing any existing file with the same name.
  */
 void
 KeepFileRestoredFromArchive(const char *path, const char *xlogfname)

src/backend/commands/analyze.c

@@ -2888,7 +2888,7 @@ analyze_mcv_list(int *mcv_counts,
 	 * significantly more common than the estimated selectivity they would
 	 * have if they weren't in the list.  All non-MCV values are assumed to be
 	 * equally common, after taking into account the frequencies of all the
-	 * the values in the MCV list and the number of nulls (c.f. eqsel()).
+	 * values in the MCV list and the number of nulls (c.f. eqsel()).
 	 *
 	 * Here sumcount tracks the total count of all but the last (least common)
 	 * value in the MCV list, allowing us to determine the effect of excluding

src/backend/commands/seclabel.c

@@ -321,7 +321,7 @@ SetSharedSecurityLabel(const ObjectAddress *object,
 /*
  * SetSecurityLabel attempts to set the security label for the specified
  * provider on the specified object to the given value.  NULL means that any
- * any existing label should be deleted.
+ * existing label should be deleted.
  */
 void
 SetSecurityLabel(const ObjectAddress *object,

src/backend/libpq/be-secure-openssl.c

@@ -956,8 +956,8 @@ info_cb(const SSL *ssl, int type, int args)
  * precomputed.
  *
  * Since few sites will bother to create a parameter file, we also
- * also provide a fallback to the parameters provided by the
- * OpenSSL project.
+ * provide a fallback to the parameters provided by the OpenSSL
+ * project.
  *
  * These values can be static (once loaded or computed) since the
  * OpenSSL library can efficiently generate random keys from the

src/backend/partitioning/partprune.c

@@ -2483,7 +2483,7 @@ get_matching_range_bounds(PartitionPruneContext *context,
 
 	/*
 	 * If the query does not constrain all key columns, we'll need to scan the
-	 * the default partition, if any.
+	 * default partition, if any.
 	 */
 	if (nvalues < partnatts)
 		result->scan_default = partition_bound_has_default(boundinfo);

src/backend/storage/ipc/barrier.c

@@ -115,7 +115,7 @@ BarrierInit(Barrier *barrier, int participants)
  *
  * While waiting, pg_stat_activity shows a wait_event_class and wait_event
  * controlled by the wait_event_info passed in, which should be a value from
- * from one of the WaitEventXXX enums defined in pgstat.h.
+ * one of the WaitEventXXX enums defined in pgstat.h.
  *
  * Return true in one arbitrarily chosen participant.  Return false in all
  * others.  The return code can be used to elect one participant to execute a

src/backend/utils/adt/datetime.c

@@ -1144,8 +1144,8 @@ DecodeDateTime(char **field, int *ftype, int nf,
 					 * Is this a YMD or HMS specification, or a year number?
 					 * YMD and HMS are required to be six digits or more, so
 					 * if it is 5 digits, it is a year.  If it is six or more
-					 * more digits, we assume it is YMD or HMS unless no date
-					 * and no time values have been specified.  This forces 6+
+					 * digits, we assume it is YMD or HMS unless no date and
+					 * no time values have been specified.  This forces 6+
 					 * digit years to be at the end of the string, or to use
 					 * the ISO date specification.
 					 */