cythonize: do not require .pyx file to be first in extension.sources

--HG--
extra : transplant_source : Dm%10%1E%DC%25%CFl%B4%E9%95%9A%1E%86%3A%FE%A4%60%BF%C3

Cython/Build/Dependencies.py

@@ -603,8 +603,10 @@ def create_extension_list(patterns, exclude=[], ctx=None, aliases=None, quiet=Fa
             base = None
             exn_type = Extension
         elif isinstance(pattern, Extension):
-            filepattern = pattern.sources[0]
-            if os.path.splitext(filepattern)[1] not in ('.py', '.pyx'):
+            for filepattern in pattern.sources:
+                if os.path.splitext(filepattern)[1] in ('.py', '.pyx'):
+                    break
+            else:
                 # ignore non-cython modules
                 module_list.append(pattern)
                 continue