add one file for VC 2013

vsprojects/libprotoc.vcproj

@@ -223,6 +223,10 @@
 				RelativePath="..\src\google\protobuf\compiler\cpp\cpp_string_field.h"
 				>
 			</File>
+			<File
+				RelativePath="..\src\google\protobuf\compiler\java\java_context.h"
+				>
+			</File>
 			<File
 				RelativePath="..\src\google\protobuf\compiler\java\java_enum.h"
 				>
@@ -383,6 +387,10 @@
 				RelativePath="..\src\google\protobuf\compiler\cpp\cpp_string_field.cc"
 				>
 			</File>
+			<File
+				RelativePath="..\src\google\protobuf\compiler\java\java_context.cc"
+				>
+			</File>
 			<File
 				RelativePath="..\src\google\protobuf\compiler\java\java_enum.cc"
 				>