s/pobjc/pbobjc and simplify a bit the podspec

Protobuf.podspec

@@ -6,13 +6,24 @@ Pod::Spec.new do |s|
   s.license  = 'New BSD'
   s.authors  = { 'The Protocol Buffers contributors' => 'protobuf@googlegroups.com' }
 
-  s.source_files = 'objectivec/*.{h,m}', 'objectivec/google/protobuf/*.pbobjc.h', 'objectivec/google/protobuf/Any.pbobjc.m', 'objectivec/google/protobuf/Api.pbobjc.m', 'objectivec/google/protobuf/Descriptor.pbobjc.m', 'objectivec/google/protobuf/Empty.pbobjc.m', 'objectivec/google/protobuf/FieldMask.pbobjc.m', 'objectivec/google/protobuf/SourceContext.pbobjc.m', 'objectivec/google/protobuf/Struct.pbobjc.m' 'objectivec/google/protobuf/Type.pbobjc.m', 'objectivec/google/protobuf/Wrappers.pbobjc.m'
+  s.source_files = 'objectivec/*.{h,m}', \
+                   'objectivec/google/protobuf/Any.pbobjc.{h,m}', \
+                   'objectivec/google/protobuf/Descriptor.pbobjc.{h,m}', \
+                   'objectivec/google/protobuf/Duration.pbobjc.h', \
+                   'objectivec/google/protobuf/Empty.pbobjc.{h,m}', \
+                   'objectivec/google/protobuf/FieldMask.pbobjc.{h,m}', \
+                   'objectivec/google/protobuf/SourceContext.pbobjc.{h,m}', \
+                   'objectivec/google/protobuf/Struct.pbobjc.{h,m}', \
+                   'objectivec/google/protobuf/Timestamp.pbobjc.h', \
+                   'objectivec/google/protobuf/Wrappers.pbobjc.{h,m}'
   # The following would cause duplicate symbol definitions
-  s.exclude_files = 'objectivec/GPBProtocolBuffers.m', 'objectivec/google/protobuf/Api.pobjc.m', 'objectivec/google/protobuf/Type.pobjc.m'
+  s.exclude_files = 'objectivec/GPBProtocolBuffers.m', \
+                    'objectivec/google/protobuf/Api.pbobjc.{h,m}', \
+                    'objectivec/google/protobuf/Type.pbobjc.{h,m}'
   # The .m's of the proto Well-Known-Types under google/protobuf are #imported
   # by GPBWellKnownTypes.m. So we can't compile them (duplicate symbols), but we
   # need them available for the importing:
-  s.preserve_paths = 'objectivec/google/protobuf/*.pbobjc.m'
+  s.preserve_paths = 'objectivec/google/protobuf/Timestamp.pbobjc.m', 'objectivec/google/protobuf/Duration.pbobjc.m'
   s.header_mappings_dir = 'objectivec'
 
   s.ios.deployment_target = '6.0'