Added a PIL alpha_over extension in C, and code to setup.py to build it

I needed a way to let py2exe options be provided only when py2exe is
available. My solution (maybe not the best) was to put all the
arguments for the final setup() call into a dictionary, that is filled
in conditionally during the script's execution. This is why the file
is completely changed; however, it still does what it used to do (when
py2exe is available).

setup.py

@@ -1,13 +1,68 @@
-from distutils.core import setup
-import py2exe
+from distutils.core import setup, Extension
+from distutils.command.build import build
+from distutils.command.clean import clean
+from distutils.dir_util import remove_tree
+from distutils import log
+import os, os.path
 
-setup(console=['gmap.py'],
-        data_files=[('textures', ['textures/lava.png', 'textures/water.png']),
-		('', ['template.html'])],
-        zipfile = None,
-        options = {'py2exe': {
-            'bundle_files': 1,
-            }},
+try:
+    import py2exe
+except ImportError:
+    py2exe = None
+
+# now, setup the keyword arguments for setup
+# (because we don't know until runtime if py2exe is available)
+setup_kwargs = {}
+setup_kwargs['options'] = {}
+setup_kwargs['ext_modules'] = []
+setup_kwargs['cmdclass'] = {}
+
+#
+# py2exe options
+#
+
+if py2exe != None:
+    setup_kwargs['console'] = ['gmap.py']
+    setup_kwargs['data_files'] = [('textures', ['textures/lava.png', 'textures/water.png']),
+                                  ('', ['template.html'])]
+    setup_kwargs['zipfile'] = None
+    setup_kwargs['options']['py2exe'] = {'bundle_files' : 1}
+
+#
+# _composite.c extension
+#
+
+setup_kwargs['ext_modules'].append(Extension('_composite', ['_composite.c']))
+# tell build_ext to build the extension in-place
+# (NOT in build/)
+setup_kwargs['options']['build_ext'] = {'inplace' : 1}
+# tell the build command to only run build_ext
+build.sub_commands = [('build_ext', None)]
+
+# custom clean command to remove in-place extension
+class CustomClean(clean):
+    def run(self):
+        # do the normal cleanup
+        clean.run(self)
         
-        
-	)
+        # try to remove '_composite.{so,pyd,...}' extension,
+        # regardless of the current system's extension name convention
+        build_ext = self.get_finalized_command('build_ext')
+        fname = build_ext.get_ext_fullpath('_composite')
+        pretty_fname = os.path.split(fname)[1]
+        if os.path.exists(fname):
+            try:
+                if not self.dry_run:
+                    os.remove(fname)
+                log.info("removing '%s'", pretty_fname)
+            except OSError:
+                log.warn("'%s' could not be cleaned -- permission denied",
+                         pretty_fname)
+        else:
+            log.debug("'%s' does not exist -- can't clean it",
+                      pretty_fname)
+setup_kwargs['cmdclass']['clean'] = CustomClean
+
+###
+
+setup(**setup_kwargs)