Add patch for problem with python module suffixes.

ndarray now uses on pybind11's cmake tools to build its Python
test module, and those don't seem to get the suffix right in
pybind11 2.1.x.

This patch can be removed once we've upgraded to pybind11 2.2.x.

patches/050-pymodule-suffix.patch

@@ -0,0 +1,16 @@
+diff -ru ndarray-1.4.0.orig/tests/CMakeLists.txt ndarray-1.4.0/tests/CMakeLists.txt
+--- ndarray-1.4.0.orig/tests/CMakeLists.txt	2018-02-12 14:41:13.000000000 -0500
++++ ndarray-1.4.0/tests/CMakeLists.txt	2018-02-12 16:41:39.023079756 -0500
+@@ -88,6 +88,12 @@
+
+         include_directories(${PYBIND11_INCLUDE_DIR})
+
++        # Either pybind11 2.1.x doesn't set the module extension appropriately,
++        # or ndarray is inadvertently squashing it.  In any case, the problem
++        # goes away with pybind11 2.2.x, and in the meantime this fixes it.
++        # It probably wouldn't work on Windows, but we don't care about that.
++        set(PYTHON_MODULE_EXTENSION ".so")
++
+         pybind11_add_module(pybind11_test_mod pybind11_test_mod.cc)
+
+         configure_file(pybind11_test.py pybind11_test.py COPYONLY)