Use swig if available, but package wiringpi_wrap.c in the source dist.

MANIFEST.in

@@ -4,3 +4,5 @@ include LICENSE.txt
 include bindings.i
 include constants.py
 include wiringpi-class.py
+include wiringpi.i
+include wiringpi_wrap.c

setup.py

@@ -1,12 +1,27 @@
 #!/usr/bin/env python
 
+import os
+import sys
+
 from setuptools import setup, Extension
 from setuptools.command.build_py import build_py
+from setuptools.command.sdist import sdist
+from distutils.spawn import find_executable
 from glob import glob
 
 sources = glob('WiringPi/devLib/*.c')
 sources += glob('WiringPi/wiringPi/*.c')
-sources += ['wiringpi.i']
+# If we have swig, use it.  Otherwise, use the pre-generated
+# wrapper from the source distribution.
+if find_executable('swig'):
+    sources += ['wiringpi.i']
+elif os.path.exists('wiringpi_wrap.c'):
+    sources += ['wiringpi_wrap.c']
+else:
+    print("Error:  Building this module requires either that swig is installed\n"
+          "        (e.g., 'sudo apt install swig') or that wiringpi_wrap.c from the\n"
+          "        source distribution (on pypi) is available.")
+    sys.exit(1)
 
 try:
     sources.remove('WiringPi/devLib/piFaceOld.c')
@@ -22,12 +37,19 @@ except ValueError:
 #  https://stackoverflow.com/a/29551581/7938656
 #  and
 #  https://blog.niteoweb.com/setuptools-run-custom-code-in-setup-py/
-class Build_ext_first(build_py):
+class build_py_ext_first(build_py):
     def run(self):
         self.run_command("build_ext")
         return build_py.run(self)
 
 
+# Make sure wiringpi_wrap.c is available for the source dist, also.
+class sdist_ext_first(sdist):
+    def run(self):
+        self.run_command("build_ext")
+        return sdist.run(self)
+
+
 _wiringpi = Extension(
     '_wiringpi',
     include_dirs=['WiringPi/wiringPi','WiringPi/devLib'],
@@ -37,9 +59,9 @@ _wiringpi = Extension(
 
 setup(
     name = 'wiringpi',
-    version = '2.44.3',
+    version = '2.44.4',
     ext_modules = [ _wiringpi ],
     py_modules = ["wiringpi"],
     install_requires=[],
-    cmdclass = {'build_py' : Build_ext_first},
+    cmdclass = {'build_py' : build_py_ext_first, 'sdist' : sdist_ext_first},
 )