Fixed a few showstoppers in the process of making MacPython use setup.py to...

Fixed a few showstoppers in the process of making MacPython use setup.py to build it's exension modules (in stead of relying on a private mechanism). It definitely doesn't work yet, but it looks promising.

setup.py

@@ -18,7 +18,7 @@ def add_dir_to_list(dirlist, dir):
     """Add the directory 'dir' to the list 'dirlist' (at the front) if
     1) 'dir' is not already in 'dirlist'
     2) 'dir' actually exists, and is a directory."""
-    if os.path.isdir(dir) and dir not in dirlist:
+    if dir is not None and os.path.isdir(dir) and dir not in dirlist:
         dirlist.insert(0, dir)
 
 def find_file(filename, std_dirs, paths):
@@ -99,7 +99,7 @@ class PyBuildExt(build_ext):
 
         # Platform-dependent module source and include directories
         platform = self.get_platform()
-        if platform == 'darwin':
+        if platform in ('darwin', 'mac'):
             # Mac OS X also includes some mac-specific modules
             macmoddir = os.path.join(os.getcwd(), srcdir, 'Mac/Modules')
             moddirlist.append(macmoddir)
@@ -126,6 +126,7 @@ class PyBuildExt(build_ext):
             if ext.name in sys.builtin_module_names:
                 self.extensions.remove(ext)
 
+        if platform != 'mac':
             # Parse Modules/Setup to figure out which modules are turned
             # on in the file.
             input = text_file.TextFile('Modules/Setup', join_lines=1)
@@ -258,7 +259,7 @@ class PyBuildExt(build_ext):
 
         # Check for MacOS X, which doesn't need libm.a at all
         math_libs = ['m']
-        if platform in ['darwin', 'beos']:
+        if platform in ['darwin', 'beos', 'mac']:
             math_libs = []
 
         # XXX Omitted modules: gl, pure, dl, SGI-specific modules