Changed piecewise body, fixes #331
As seen in test_simple, when `x` has more than one element
the condlist `[True, False]` is being made equivalent to
`[[True, False]]`, which is correct. However, when `x` is
zero dimensional the expected condlist is `[[True], [False]]`
(see 1cce6e4). Therefore, when a 0d array is given the transpose
is used.