[IMP] util/misc: cache unique functions

Improves caching to not simply cache the result of the first
call of a function, but each *unique* (based on args and kwargs,
taking into consideration their order) call.

src/util/misc.py

@@ -30,17 +30,17 @@
 
 
 def _cached(func):
-    sentinel = object()
+    func._cache = {}
 
     @functools.wraps(func)
     def wrapper(*args, **kwargs):
-        result = getattr(func, "_result", sentinel)
-        if result == sentinel:
-            result = func._result = func(*args, **kwargs)
-        return result
+        key = (args, tuple(sorted(kwargs.items())))
 
-    return wrapper
+        if key not in func._cache:
+            func._cache[key] = func(*args, **kwargs)
+        return func._cache[key]
 
+    return wrapper
 
 # copied from odoo as older OpenERP versions doesn't have it
 def str2bool(s, default=None):