Pull new version of protobuf sources.

third_party/protobuf/Protobuf.podspec

+# This file describes to Cocoapods how to integrate the Objective-C runtime into a dependent
+# project.
+# Despite this file being specific to Objective-C, it needs to be on the root of the repository.
+# Otherwise, Cocoapods gives trouble like not picking up the license file correctly, or not letting
+# dependent projects use the :git notation to refer to the library.
+Pod::Spec.new do |s|
+  s.name     = 'Protobuf'
+  s.version  = '3.0.0-alpha-4-pre'
+  s.summary  = 'Protocol Buffers v.3 runtime library for Objective-C.'
+  s.homepage = 'https://github.com/google/protobuf'
+  s.license  = 'New BSD'
+  s.authors  = { 'The Protocol Buffers contributors' => 'protobuf@googlegroups.com' }
+
+  s.source_files = 'objectivec/GPBProtocolBuffers.{h,m}'
+  # GPBProtocolBuffers.{h,m} are umbrella files. We need Cocoapods to preserve the files imported by
+  # them.
+  s.preserve_paths = 'objectivec/*.{h,m}',
+                     'objectivec/google/protobuf/*.pbobjc.{h,m}'
+  s.header_mappings_dir = 'objectivec'
+
+  s.ios.deployment_target = '7.1'
+  s.osx.deployment_target = '10.9'
+  s.requires_arc = false
+end