pg_is_xlog_replay_paused(): remove super-user-only restriction

Also update docs to mention which function are super-user-only.

Report by sys-milan@statpro.com

Backpatch through 9.4

doc/src/sgml/func.sgml

@@ -16471,7 +16471,7 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
         <literal><function>pg_xlog_replay_pause()</function></literal>
         </entry>
        <entry><type>void</type></entry>
-       <entry>Pauses recovery immediately.
+       <entry>Pauses recovery immediately (restricted to superusers).
        </entry>
       </row>
       <row>
@@ -16479,7 +16479,7 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
         <literal><function>pg_xlog_replay_resume()</function></literal>
         </entry>
        <entry><type>void</type></entry>
-       <entry>Restarts recovery if it was paused.
+       <entry>Restarts recovery if it was paused (restricted to superusers).
        </entry>
       </row>
      </tbody>
@@ -16587,7 +16587,7 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
     for controlling and interacting with replication features.
     See <xref linkend="streaming-replication">
     and <xref linkend="streaming-replication-slots"> for information about the
-    underlying features.
+    underlying features.  Use of these functions is restricted to superusers.
    </para>
 
    <para>

src/backend/access/transam/xlogfuncs.c

@@ -382,11 +382,6 @@ pg_xlog_replay_resume(PG_FUNCTION_ARGS)
 Datum
 pg_is_xlog_replay_paused(PG_FUNCTION_ARGS)
 {
-	if (!superuser())
-		ereport(ERROR,
-				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 (errmsg("must be superuser to control recovery"))));
-
 	if (!RecoveryInProgress())
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),