Support the PBMessage_Builder protocol.

PBUnknownFieldSet_Builder needs to conform to the PBMessage_Builder
protocol in order for it to be used in all of the places expecting
id<PBMessage_Builder> values.

The protocol itself is pretty heavy, and some of the methods could be
made @optional, but for now we just raise exceptions for unsupported
calls (which is consistent with the rest of the runtime library).

This fixes the Apple LLVM compiler 3.0 warnings reported in #16.

src/runtime/Classes/UnknownFieldSet_Builder.h

@@ -15,7 +15,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-@interface PBUnknownFieldSet_Builder : NSObject {
+#import "Message_Builder.h"
+
+@interface PBUnknownFieldSet_Builder : NSObject <PBMessage_Builder> {
 @private
   NSMutableDictionary* fields;
 

src/runtime/Classes/UnknownFieldSet_Builder.m

@@ -117,6 +117,29 @@ - (PBUnknownFieldSet*) build {
   return result;
 }
 
+- (PBUnknownFieldSet*) buildPartial {
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
+}
+
+- (PBUnknownFieldSet*) clone {
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
+}
+
+- (BOOL) isInitialized {
+  return YES;
+}
+
+- (PBUnknownFieldSet*) defaultInstance {
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
+}
+
+- (PBUnknownFieldSet*) unknownFields {
+  return [self build];
+}
+
+- (id<PBMessage_Builder>) setUnknownFields:(PBUnknownFieldSet*) unknownFields {
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
+}
 
 /** Check if the given field number is present in the set. */
 - (BOOL) hasField:(int32_t) number {
@@ -168,10 +191,21 @@ - (PBUnknownFieldSet_Builder*) mergeFromData:(NSData*) data {
 }
 
 
+- (PBUnknownFieldSet_Builder*) mergeFromData:(NSData*) data extensionRegistry:(PBExtensionRegistry*) extensionRegistry {
+  PBCodedInputStream* input = [PBCodedInputStream streamWithData:data];
+  [self mergeFromCodedInputStream:input extensionRegistry:extensionRegistry];
+  [input checkLastTagWas:0];
+  return self;
+}
+
+
 - (PBUnknownFieldSet_Builder*) mergeFromInputStream:(NSInputStream*) input {
-  @throw [NSException exceptionWithName:@"" reason:@"" userInfo:nil];
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
 }
 
+- (PBUnknownFieldSet_Builder*) mergeFromInputStream:(NSInputStream*) input extensionRegistry:(PBExtensionRegistry*) extensionRegistry {
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
+}
 
 - (PBUnknownFieldSet_Builder*) mergeVarintField:(int32_t) number value:(int32_t) value {
   if (number == 0) {
@@ -231,6 +265,9 @@ - (PBUnknownFieldSet_Builder*) mergeFromCodedInputStream:(PBCodedInputStream*) i
   return self;
 }
 
+- (PBUnknownFieldSet_Builder*) mergeFromCodedInputStream:(PBCodedInputStream*) input extensionRegistry:(PBExtensionRegistry*) extensionRegistry {
+  @throw [NSException exceptionWithName:@"UnsupportedMethod" reason:@"" userInfo:nil];
+}
 
 - (PBUnknownFieldSet_Builder*) clear {
   self.fields = [NSMutableDictionary dictionary];