BUG: Fix GeoSeries constructor for multi geoms

Because Multi* geometries are iterable, they get expanded when passed into
np.array(). Protect against this by passing in all base geometries as a
single element list. They will not be expanded into their individual
parts.

Switch on older versions of pandas when Series overrode __new__ instead
of __init__.
TST: Test GeoSeries constructor with index

Make sure that when a single geometry is passed in and the index contains
multiple elements, the geometry is replicated in the GeoSeries.

As suggested by @jtratner in Issue #70.