Changes to build to fix creation of wheels. (#840)

* Pass DPYTHON_EXECUTABLE into cmake for arrow and for ray.

* Add cython to setup.py install_requires.

* Revert custom code for finding python in cmake.

* Correctly find arrow on CentOS.

* In cmake, don't find PythonLibs, just find PYTHON_INCLUDE_DIRS.

* Fix typo.

* Do not use boost shared libraries when building arrow.

* Add six to the setup.py install_requires because it is needed by pyarrow.

* Don't link numbuf against boost_system and boost_filesystem.

* Compile boost when we are on Linux.

* Make numbuf find the correct boost libraries.

* Only use find_package Boost on Linux, suppress output when building boost.

* Changes to wheel building scripts, install cython in mac script.

* Compile flatbuffers ourselves on Linux and pass it in when compiling Arrow.

* Clean up build_flatbuffers.sh and build_boost.sh scripts a little.

* Install cython when building linux wheel.

cmake/Modules/FindNumPy.cmake

@@ -14,8 +14,8 @@
 unset(NUMPY_VERSION)
 unset(NUMPY_INCLUDE_DIR)
 
-if(NOT "${CUSTOM_PYTHON_EXECUTABLE}" STREQUAL "CUSTOM_PYTHON_EXECUTABLE-NOTFOUND")
-  execute_process(COMMAND "${CUSTOM_PYTHON_EXECUTABLE}" "-c"
+if(PYTHONINTERP_FOUND)
+  execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c"
     "import numpy as n; print(n.__version__); print(n.get_include());"
     RESULT_VARIABLE __result
     OUTPUT_VARIABLE __output
@@ -42,7 +42,7 @@ if(NOT "${CUSTOM_PYTHON_EXECUTABLE}" STREQUAL "CUSTOM_PYTHON_EXECUTABLE-NOTFOUND
     endif()
   endif()
 else()
-  message(STATUS "To find NumPy Python executable is required to be found.")
+  message(STATUS "To find NumPy Python interpreter is required to be found.")
 endif()
 
 include(FindPackageHandleStandardArgs)