[FIX] base: avoid deleting translations

When updating a translation, the previous one is deleted and a new one is
recreated (with no module and state). When the source module is updated, the
previous term is inserted again to the lsit of terms.
Instead of dropping and recreating terms during update, simply update the
existing term and create one only if there were no previous translation.
Fixes #4617

openerp/addons/base/ir/ir_translation.py

@@ -286,21 +286,31 @@ class ir_translation(osv.osv):
     def _set_ids(self, cr, uid, name, tt, lang, ids, value, src=None):
         self._get_ids.clear_cache(self)
         self.__get_source.clear_cache(self)
-
-        cr.execute('delete from ir_translation '
+        original_module = self.pool[name.split(',')[0]]._original_module
+        cr.execute('update ir_translation '
+                  'set value=%s '
+                  '  , src=%s '
+                  '  , state=%s '
                 'where lang=%s '
                     'and type=%s '
                     'and name=%s '
-                    'and res_id IN %s',
-                (lang,tt,name,tuple(ids),))
-        for id in ids:
+                    'and module=%s '
+                    'and res_id IN %s '
+                'returning res_id',
+                (value,src,'translated',lang,tt,name,original_module,tuple(ids),))
+
+        existing_ids = [x[0] for x in cr.fetchall()]
+
+        for id in list(set(ids) - set(existing_ids)):
             self.create(cr, uid, {
                 'lang':lang,
                 'type':tt,
                 'name':name,
                 'res_id':id,
+                'module':original_module,
                 'value':value,
                 'src':src,
+                'state':'translated'
                 })
         return len(ids)