Doc: clarify behavior of back-half options in pg_dump.

Options that change how the archive data is converted to SQL text
are ignored when dumping to archive formats.  The documentation
previously said "not meaningful", which is not helpful.

Discussion: https://postgr.es/m/161052021249.12228.9598689907884726185@wrigleys.postgresql.org

doc/src/sgml/ref/pg_dump.sgml

@@ -176,8 +176,8 @@ PostgreSQL documentation
        </para>
 
        <para>
-        This option is only meaningful for the plain-text format.  For
-        the archive formats, you can specify the option when you
+        This option is ignored when emitting an archive (non-text) output
+        file.  For the archive formats, you can specify the option when you
         call <command>pg_restore</command>.
        </para>
       </listitem>
@@ -208,8 +208,8 @@ PostgreSQL documentation
        </para>
 
        <para>
-        This option is only meaningful for the plain-text format.  For
-        the archive formats, you can specify the option when you
+        This option is ignored when emitting an archive (non-text) output
+        file.  For the archive formats, you can specify the option when you
         call <command>pg_restore</command>.
        </para>
       </listitem>
@@ -456,8 +456,8 @@ PostgreSQL documentation
        </para>
 
        <para>
-        This option is only meaningful for the plain-text format.  For
-        the archive formats, you can specify the option when you
+        This option is ignored when emitting an archive (non-text) output
+        file.  For the archive formats, you can specify the option when you
         call <command>pg_restore</command>.
        </para>
       </listitem>
@@ -693,8 +693,8 @@ PostgreSQL documentation
        </para>
 
        <para>
-        This option is only meaningful for the plain-text format.  For
-        the archive formats, you can specify the option when you
+        This option is ignored when emitting an archive (non-text) output
+        file.  For the archive formats, you can specify the option when you
         call <command>pg_restore</command>.
        </para>
       </listitem>
@@ -924,8 +924,8 @@ PostgreSQL documentation
        </para>
 
        <para>
-        This option is only meaningful for the plain-text format.  For
-        the archive formats, you can specify the option when you
+        This option is ignored when emitting an archive (non-text) output
+        file.  For the archive formats, you can specify the option when you
         call <command>pg_restore</command>.
        </para>
       </listitem>