gracefully skip C extension if it can't be built

git-svn-id: svn://svn.code.sf.net/p/fonttools/code/trunk@274 4cde692c-a291-49d1-8350-778aa11640f8

setup.py

@@ -2,6 +2,7 @@
 
 import os, sys
 from distutils.core import setup, Extension
+from distutils.command.build_ext import build_ext
 
 
 try:
@@ -17,6 +18,19 @@ except ImportError:
 	print "        http://sourceforge.net/projects/pyxml/"
 
 
+class build_ext_optional(build_ext):
+	"""build_ext command which doesn't abort when it fails."""
+	def build_extension(self, ext):
+		# Skip extensions which cannot be built
+		try:
+			build_ext.build_extension(self, ext)
+		except:
+			self.announce(
+				'*** WARNING: Building of extension "%s" '
+				'failed: %s' %
+				(ext.name, sys.exc_info()[1]))
+
+
 setup(
 		name = "FontTools",
 		version = "1.0",
@@ -49,5 +63,6 @@ setup(
 			)
 		],
 		scripts = ["Tools/ttcompile", "Tools/ttdump", "Tools/ttlist"],
+		cmdclass = {"build_ext": build_ext_optional}
 	)