Doc: clarify description of CREATE/ALTER FUNCTION ... SET FROM CURRENT.

Per discussion with David Johnston.

doc/src/sgml/ref/alter_function.sgml

@@ -225,8 +225,9 @@ ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="paramet
         setting is removed, so that the function executes with the value
         present in its environment.  Use <literal>RESET
         ALL</literal> to clear all function-local settings.
-        <literal>SET FROM CURRENT</> saves the session's current value of
+        <literal>SET FROM CURRENT</> saves the value of the parameter that
-        the parameter as the value to be applied when the function is entered.
+        is current when <command>ALTER FUNCTION</> is executed as the value
+        to be applied when the function is entered.
        </para>
 
        <para>

doc/src/sgml/ref/create_function.sgml

@@ -399,8 +399,9 @@ CREATE [ OR REPLACE ] FUNCTION
        The <literal>SET</> clause causes the specified configuration
        parameter to be set to the specified value when the function is
        entered, and then restored to its prior value when the function exits.
-       <literal>SET FROM CURRENT</> saves the session's current value of
+       <literal>SET FROM CURRENT</> saves the value of the parameter that
-       the parameter as the value to be applied when the function is entered.
+       is current when <command>CREATE FUNCTION</> is executed as the value
+       to be applied when the function is entered.
       </para>
 
       <para>