[IMP] config: deduplicate loggers in log_handler

Saving multiple levels for the same logger should work with few issues,
but over time pathological (basket) cases (e.g. using ``-s`` all the
time) may build pointlessly huge lists in their config file.

Only keep the last level for each logger when saving to a config file.

openerp/tools/config.py

@@ -623,7 +623,7 @@ class configmanager(object):
             if opt in ('log_level',):
                 p.set('options', opt, loglevelnames.get(self.options[opt], self.options[opt]))
             elif opt == 'log_handler':
-                p.set('options', opt, ','.join(self.options[opt]))
+                p.set('options', opt, ','.join(deduplicate_loggers(self.options[opt])))
             else:
                 p.set('options', opt, self.options[opt])
 
@@ -686,5 +686,18 @@ class configmanager(object):
 
 config = configmanager()
 
+def deduplicate_loggers(loggers):
+    """ Avoid saving multiple logging levels for the same loggers to a save
+    file, that just takes space and the list can potentially grow unbounded
+    if for some odd reason people use :option`odoo.py --save`` all the time.
+    """
+    # dict(iterable) -> the last item of iterable for any given key wins,
+    # which is what we want and expect. Output order should not matter as
+    # there are no duplicates within the output sequence
+    return (
+        '{}:{}'.format(logger, level)
+        for logger, level in dict(it.split(':') for it in loggers).iteritems()
+    )
+
 
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