BUG: remove wraparound in cython.wraparound(False) function

with cython 0.19 you get this warning:

warning: scipy/spatial/ckdtree.pyx:1212:24: the result of using negative indices inside of code sections marked as 'wraparound=False' is undefined
warning: scipy/spatial/ckdtree.pyx:1222:33: the result of using negative indices inside of code sections marked as 'wraparound=False' is undefined