Fix doc double-wording in non-durable patch.

Report from Thom Brown

doc/src/sgml/config.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.284 2010/06/28 21:57:17 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/config.sgml,v 1.285 2010/06/28 22:46:11 momjian Exp $ -->
 
 <chapter Id="runtime-config">
   <title>Server Configuration</title>
@@ -1464,7 +1464,7 @@ SET ENABLE_SEQSCAN TO OFF;
         delay is three times <xref linkend="guc-wal-writer-delay">.)  Unlike
         <xref linkend="guc-fsync">, setting this parameter to <literal>off</>
         does not create any risk of database inconsistency: an operating
-        system or database crash crash might
+        system or database crash might
         result in some recent allegedly-committed transactions being lost, but
         the database state will be just the same as if those transactions had
         been aborted cleanly.  So, turning <varname>synchronous_commit</> off

doc/src/sgml/perform.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.81 2010/06/28 21:57:17 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/perform.sgml,v 1.82 2010/06/28 22:46:11 momjian Exp $ -->
 
  <chapter id="performance-tips">
   <title>Performance Tips</title>
@@ -1113,7 +1113,7 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
 
    <para>
     Durability is a database feature that guarantees the recording of
-    committed transactions even if if the server crashes or loses
+    committed transactions even if the server crashes or loses
     power.  However, durability adds significant database overhead,
     so if your site does not require such a guarantee,
     <productname>PostgreSQL</productname> can be configured to run