BUG: Use Py_ssize_t to index into numpy arrays to help Python handle big data.
Indent a few copy/pasted function declarations for consistency.
Fixes #1466.
MISC: Update _tree.c with cython.
BUG: Use ``Py_ssize_t`` in a few more places for strides. Add the c file again.
Merge pull request #1823 from erg/issue-1466

PR for Issue #1466