Add missing plugin.h into extract_includes.bat script.
diff --git a/vsprojects/extract_includes.bat b/vsprojects/extract_includes.bat
index 5e513d7..386d204 100755
--- a/vsprojects/extract_includes.bat
+++ b/vsprojects/extract_includes.bat
@@ -40,3 +40,4 @@
copy ..\src\google\protobuf\compiler\cpp\cpp_generator.h include\google\protobuf\compiler\cpp\cpp_generator.h
copy ..\src\google\protobuf\compiler\java\java_generator.h include\google\protobuf\compiler\java\java_generator.h
copy ..\src\google\protobuf\compiler\python\python_generator.h include\google\protobuf\compiler\python\python_generator.h
+copy ..\src\google\protobuf\compiler\plugin.h include\google\protobuf\compiler\plugin.h