Apple engineers have pointed out that OSSpinLocks are vulnerable to live locking
on iOS in cases of priority inversion:
. http://mjtsai.com/blog/2015/12/16/osspinlock-is-unsafe/
. https://lists.swift.org/pipermail/swift-dev/Week-of-Mon-20151214/000372.html

- Use a dispatch_semaphore_t within the extension registry.
- Use a dispatch_semaphore_t for protecting autocreation within messages.
- Drop the custom/internal GPBString class since we don't have really good
  numbers to judge the locking replacements and it isn't required. We can
  always bring it back with real data in the future.

- Let Xcode update the projects, schemes, and info.plists.
- Add workaround for shallow analyzer issues in current Xcode versions (deep analyze gets things correct).
- Tweak the Swift based tests to avoid warnings from Xcode 7's XCTest using optionals for autoenclosure results.
- No longer tag the ObjC iOS travis test as flaky, xctool seems to manage the simulator pretty well.

- Mark all conformance tests as now passing.

- Support building with Xcode 6.4 or 7.x
- Fix an error in usage info.
- Add a flag to build the core parts of protobuf only.

- Kick off the conformance tests
- Add missing ignore for something generated by a build on the conformance directory.

NS_ENUM changes defintion in Objective C++ based on the C++ spec being
compiled with, special case the one situation where it wouldn't support doing a
forward decl for the enum.

- Move up to 8.4 as the high simulator (assuming Xcode 6.4).
- Add cast to NSMutableDictionary so clang and resolve the selector.
- Add case for the newer static analyzer so it won't trigger a false warning.
- Update the "dictionary" interface to use "object" naming. Xcode 7+ has gotten
  more strict on the use of nonnull/nullable; combining that with the generic
  collection support; and the "dictionary" classes we created now collide with
  what the generic KeyValueCoding in the system headers triggering
  warnings/errors. Fix this and hopefully all future issue by renaming the
  methods to use "object" for the classes that have data types as objects
  instead of PODs. Taking this renaming hit now while ObjC is still in beta
  because it is a breaking change for any existing code.

- Add a env var to pass a set of expected prefixes for validation.
- Report warnings/errors based on the expected prefixes vs. the data in the files compiled.
- Use some helpers from common directory.

This reverts commit 7366efd8.

Still some discussion about the api to expose the helpers with.

fix an bug(forgive my english..)

The previous two methods make it easy to transform between any and normal message.
unPackeTo will throw error if the type url in any doesn't match the type of the message to be transformed to.
is checks any's type url matches the give GPBMessage type.

Also add WKT headers to the umbrella file, and simplify Podspec with it.
Plus some layout improvements to the BUILD file.

Add the clang annotations to the objc library and generated code to help with Swift bridging and compiler checks.

- Add more to the ObjC dir readme.
- Merge the ExtensionField and ExtensionDescriptor to reduce overhead.
- Fix an initialization race.
- Clean up the Xcode schemes.
- Remove the class/enum filter.
- Remove some forced inline that were bloating things without proof of performance wins.
- Rename some internal types to avoid conflicts with the well know types protos.
- Drop the use of ApplyFunctions to the compiler/optimizer can do what it wants.
- Better document some possible future improvements.
- Add missing support for parsing repeated primitive fields in packed or unpacked forms.
- Improve -hash.
- Add *Count for repeated and map<> fields to avoid auto create when checking for them being set.

- Shouldn't need SRCROOT in the project since Xcode should be setting the working directory to where the project lives.
- Remove the packed/unpacked repeated enum field in the tests and update the code to handle the defaults.
- Move up the ignore to cover .DS_Store files in src also.

add starstar

- Style fixups in the code.
- map<> serialization fixes and more tests.
- Autocreation of map<> fields (to match repeated fields).
- @@protoc_insertion_point(global_scope|imports).
- Fixup proto2 syntax extension support.
- Move all startup code to +initialize so it happen on class usage and not app startup.
- Have generated headers use forward declarations and move imports into generated code, reduces what is need at compile time to speed up compiled and avoid pointless rippling of rebuilds.

Remove the ClassList support (maybe bring it back in the future).
Trim the includes to hopefully get a working Window build.
Add some more returns after switches for compilers that warn even when all values of the enum are handled.
Use ghtonl instead of htonl.
Change the use of [u]int(8,32)_t within the ObjC generator code to [u]int(8,32) to match the rest of the compiler.
Add objective-c generator files to Visual Studio project.

Re-add the objc prefix that got removed by accident.
Regenerate the generated descriptors (C++ and ObjC).