Make prep_status() message translatable

Hello,

The recent commit 173c97812ff made the following change:

-    prep_status("Adding \".old\" suffix to old global/pg_control");
+    prep_status("Adding \".old\" suffix to old " XLOG_CONTROL_FILE);

This change results in a message that is untranslatable, at least into
Japanese.  In addition, the file name should be quoted.

The attached patch modifies the message to use %s for XLOG_CONTROL_FILE,  
making it properly translatable.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center