Not setting precedence higher precedence than setting precedence

```
from param import Parameterized
from param import Parameter
class A(Parameterized):
question = Parameter("What is it?", doc="The question", precedence=3)
answer = Parameter(2, constant=True, doc="The answer")
ultimate_answer = Parameter(42, readonly=True, doc="The real answer")

class B(A):
question_b = Parameter("What is it?", doc="The question", precedence=1)

a = B(question="How is it?", answer="6")
```

```
Name Value Type Mode

answer 2 Parameter C RW
ultimate_answer 42 Parameter C RO
question_b 'What is it?' Parameter V RW
question 'What is it?' Parameter V RW
```

I expected question_b to be listed first, then question, then answer + ulimate answer，