Fail hard during publish if pandoc isn't available.

setup.py

@@ -56,6 +56,10 @@ version = get_version('rest_framework')
 
 
 if sys.argv[-1] == 'publish':
+    try:
+        import pypandoc
+    except ImportError:
+        print("pypandoc not installed.\nUse `pip install pypandoc`.\nExiting.")
     if os.system("pip freeze | grep wheel"):
         print("wheel not installed.\nUse `pip install wheel`.\nExiting.")
         sys.exit()