Deprecate language as a special cythonize argument.

Cython/Build/Dependencies.py

@@ -634,6 +634,8 @@ def create_dependency_tree(ctx=None, quiet=False):
 # This may be useful for advanced users?
 def create_extension_list(patterns, exclude=None, ctx=None, aliases=None, quiet=False, language=None,
                           exclude_failures=False):
+    if language is not None:
+        print('Please put "# distutils: langauge=%s" in your .pyx or .pxd file(s)' % language)
     if exclude is None:
         exclude = []
     if not isinstance(patterns, (list, tuple)):

tests/build/cpp_cythonize.srctree

@@ -10,11 +10,13 @@ from Cython.Build.Dependencies import cythonize
 from distutils.core import setup
 
 setup(
-    ext_modules = cythonize("*.pyx", language='c++'),
+    ext_modules = cythonize("*.pyx"),
 )
 
 ######## a.pyx ########
 
+# distutils: language=c++
+
 from libcpp.vector cimport vector
 
 def use_vector(L):