[FIX]:string correction for purchase

lp bug: https://launchpad.net/bugs/916485 fixed

bzr revid: ksa@tinyerp.com-20120117100836-38ecauwmtgtu2kdv

addons/purchase/wizard/purchase_installer.py

@@ -28,7 +28,7 @@ class purchase_config_wizard(osv.osv_memory):
         'default_method' : fields.selection(
             [('manual', 'Based on Purchase Order Lines'),
              ('picking', 'Based on Receptions'),
-             ('order', 'Pre-Generate Draft Invoices on Based Purchase Orders'),
+             ('order', 'Pre-Generate Draft Invoices Based on Purchase Orders'),
             ], 'Default Invoicing Control Method', required=True,
         )
     }