Fix protobuf's Python runtime and imports.

tools/protoc_wrapper/protoc_wrapper.py

Index: tools/protoc_wrapper/protoc_wrapper.py
diff --git a/tools/protoc_wrapper/protoc_wrapper.py b/tools/protoc_wrapper/protoc_wrapper.py
index 6a25de0ed5a367cfffea3fae8dc436dc355d1f49..50aee8b98061019ec361a7d2731ae05b2437efe0 100755
--- a/tools/protoc_wrapper/protoc_wrapper.py
+++ b/tools/protoc_wrapper/protoc_wrapper.py
@@ -67,6 +67,17 @@ def WriteIncludes(headers, include):
         print(line, file=f)
 
 
+def WritePythonInit(base_dir, protos):
+  def write_init_py(path):
+    if not path:
+      return
+    open(os.path.join(base_dir, path, '__init__.py'), 'a').close()
+    write_init_py(os.path.dirname(path))
+
+  for proto in protos:
+    write_init_py(os.path.dirname(proto))
+
+
 def main(argv):
   parser = argparse.ArgumentParser()
   parser.add_argument("--protoc",
@@ -136,6 +147,9 @@ def main(argv):
   if options.include:
     WriteIncludes(headers, options.include)
 
+  if options.py_out_dir:
+    WritePythonInit(options.py_out_dir, protos)
+
 
 if __name__ == "__main__":
   try: