Make spelling of "acknowledgment" consistent

I used the preferred U.S. spelling, as we do in other cases.

doc/src/sgml/high-availability.sgml

@@ -1324,14 +1324,14 @@ synchronous_standby_names = 'ANY 2 (s1, s2, s3)'
    </para>
 
    <para>
-    If primary restarts while commits are waiting for acknowledgement, those
+    If primary restarts while commits are waiting for acknowledgment, those
     waiting transactions will be marked fully committed once the primary
     database recovers.
     There is no way to be certain that all standbys have received all
     outstanding WAL data at time of the crash of the primary. Some
     transactions may not show as committed on the standby, even though
     they show as committed on the primary. The guarantee we offer is that
-    the application will not receive explicit acknowledgement of the
+    the application will not receive explicit acknowledgment of the
     successful commit of a transaction until the WAL data is known to be
     safely received by all the synchronous standbys.
    </para>

doc/src/sgml/release-10.sgml

@@ -5890,7 +5890,7 @@ This was disabled in the PG 9.6 branch so there is no commit here.
 2016-12-19 [3901fd70c] Support quorum-based synchronous replication.
 -->
       <para>
-       Allow waiting for commit acknowledgement from standby
+       Allow waiting for commit acknowledgment from standby
        servers irrespective of the order they appear in <xref
        linkend="guc-synchronous-standby-names"/> (Masahiko Sawada)
       </para>
@@ -6462,7 +6462,7 @@ This was disabled in the PG 9.6 branch so there is no commit here.
       <para>
        This is useful for checking after an abrupt disconnection whether
        your previous transaction committed and you just didn't receive
-       the acknowledgement.
+       the acknowledgment.
       </para>
      </listitem>
 

src/backend/replication/syncrep.c

@@ -268,7 +268,7 @@ SyncRepWaitForLSN(XLogRecPtr lsn, bool commit)
 
 		/*
 		 * If the postmaster dies, we'll probably never get an
-		 * acknowledgement, because all the wal sender processes will exit. So
+		 * acknowledgment, because all the wal sender processes will exit. So
 		 * just bail out.
 		 */
 		if (!PostmasterIsAlive())

src/common/pg_lzcompress.c

@@ -159,7 +159,7 @@
  *			scanned for the history add's, otherwise a literal character
  *			is omitted and only his history entry added.
  *
- *		Acknowledgements:
+ *		Acknowledgments:
  *
  *			Many thanks to Adisak Pochanayon, who's article about SLZ
  *			inspired me to write the PostgreSQL compression this way.