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 booyah#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];