Prevent building on too old a PyPy; don't build on CPython if CFFI too old.

.gitignore

@@ -12,6 +12,7 @@ gevent/_corecffi.o
 *.egg-info
 Makefile.ext
 MANIFEST
+*_flymake.py
 
 greentest/.coverage\.*
 greentest/htmlcov

setup.py

@@ -359,15 +359,22 @@ else:
     setup_kwds = {}
 
 try:
-    __import__('cffi')
+    cffi = __import__('cffi')
 except ImportError:
     setup_kwds = {}
 else:
+    _min_cffi_version = (1, 3, 0)
+    _cffi_version_is_supported = cffi.__version_info__ >= _min_cffi_version
     _kwds = {'cffi_modules': cffi_modules}
     # We already checked for PyPy on Windows above and excluded it
     if PYPY:
+        if not _cffi_version_is_supported:
+            raise Exception("PyPy 2.6.1 or higher is required")
         setup_kwds = _kwds
     elif LIBEV_EMBED and (not WIN or CFFI_WIN_BUILD_ANYWAY):
+        if not _cffi_version_is_supported:
+            print("WARNING: CFFI version 1.3.0 is required to build CFFI backend", file=sys.stderr)
+        else:
             # If we're on CPython, we can only reliably build
             # the CFFI module if we're embedding libev (in some cases
             # we wind up embedding it anyway, which may not be what the