add last ditch effort for numpy

Apparently not all distributions include a FindNumPy.cmake or similar,
even if numpy is indeed installed. This makes a second effort to find
using python itself

Signed-off-by: Kimball Thurston <kdt3rd@gmail.com>

CMakeLists.txt

@@ -138,7 +138,37 @@ if (OPENEXR_BUILD_PYTHON_LIBS)
 
   find_package(NumPy)
   if(NOT NumPy_FOUND)
-    message(WARNING "Numpy not found, PyImathNumpy will not be built")
+
+    if(NOT PYTHON_EXECUTABLE)
+      find_package(PythonInterp QUIET)
+    endif()
+    if (PYTHON_EXECUTABLE)
+      # Find out the include path
+      execute_process(
+        COMMAND "${PYTHON_EXECUTABLE}" -c
+        "from __future__ import print_function\ntry: import numpy; print(numpy.get_include(), end='')\nexcept:pass\n"
+        OUTPUT_VARIABLE py_ilmbase_numpy_path)
+      # And the version
+      execute_process(
+        COMMAND "${PYTHON_EXECUTABLE}" -c
+        "from __future__ import print_function\ntry: import numpy; print(numpy.__version__, end='')\nexcept:pass\n"
+        OUTPUT_VARIABLE py_ilmbase_numpy_version)
+
+      find_path(NUMPY_INCLUDE_DIRS numpy/arrayobject.h
+        HINTS "${py_ilmbase_numpy_path}" "${PYTHON_INCLUDE_PATH}" NO_DEFAULT_PATH)
+
+      if(NUMPY_INCLUDE_DIRS)
+        set(NumPy_FOUND 1 CACHE INTERNAL "Python numpy found")
+
+        include(FindPackageHandleStandardArgs)
+        find_package_handle_standard_args(NumPy REQUIRED_VARS NUMPY_INCLUDE_DIRS
+          VERSION_VAR py_ilmbase_numpy_version)
+      else()
+        message(WARNING "Numpy not found, PyImathNumpy will not be built")
+      endif()
+    else ()
+      message(WARNING "Numpy not found, PyImathNumpy will not be built")
+    endif ()
   endif()
 endif()