doc: Fix some grammar and inconsistencies

Some comments are fixed while on it.

Author: Justin Pryzby
Discussion: https://postgr.es/m/20200818171702.GK17022@telsasoft.com
Backpatch-through: 9.6

doc/src/sgml/logicaldecoding.sgml

@@ -223,7 +223,7 @@ $ pg_recvlogical -d postgres --slot test --drop-slot
      A logical slot will emit each change just once in normal operation.
      The current position of each slot is persisted only at checkpoint, so in
      the case of a crash the slot may return to an earlier LSN, which will
-     then cause recent changes to be resent when the server restarts.
+     then cause recent changes to be sent again when the server restarts.
      Logical decoding clients are responsible for avoiding ill effects from
      handling the same message more than once.  Clients may wish to record
      the last LSN they saw when decoding and skip over any repeated data or

doc/src/sgml/sources.sgml

@@ -359,7 +359,7 @@ ereport(ERROR,
      specify suppression of the <literal>CONTEXT:</> portion of a message in
      the postmaster log.  This should only be used for verbose debugging
      messages where the repeated inclusion of context would bloat the log
-     volume too much.
+     too much.
     </para>
    </listitem>
   </itemizedlist>

src/backend/storage/lmgr/proc.c

@@ -1306,7 +1306,7 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 			else
 				LWLockRelease(ProcArrayLock);
 
-			/* prevent signal from being resent more than once */
+			/* prevent signal from being sent again more than once */
 			allow_autovacuum_cancel = false;
 		}