where function with implicit booleans

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The following edge cases is not correctly handled by the numexpr 'where' 
function. Basically, implicit booleans (using 1 as True) are not handled as 
they are handled in numpy.

import numexpr as ne
import numpy as np

>> np.where(1, 2, 3)
array(2)

>> ne.evaluate('where(1, 2, 3)')
Traceback (most recent call last):
...
ValueError: too many dimensions

>> a = np.array([1])
>> b = 2
>> c = 3
>> np.where(a, b, c)
array([2])

>> ne.evaluate('where(a, b, c)')
Traceback (most recent call last):
...
NotImplementedError: couldn't find matching opcode for 'where_llll'

Original issue reported on code.google.com by hyuki...@gmail.com on 9 Oct 2011 at 3:15