Parser will no longer choke when using keywords as field names, but this
practice is highly discouraged.

com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext

diff --git a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
index 2a9b65c..63e6b96 100644
--- a/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
+++ b/com.google.eclipse.protobuf/src/com/google/eclipse/protobuf/Protobuf.xtext
@@ -177,7 +177,7 @@
   MessageOptionField | '(' ExtensionOptionField ')';
 
 MessageOptionField:
-  target=[IndexedElement];  
+  target=[IndexedElement|Name];  
 
 ExtensionOptionField:
   target=[IndexedElement|QualifiedName];