This fixes issue #1730.

Update version number to 3.0.0-beta-4

Comment out lite conformance test.

The 'lite' generator flag is no longer supported.

Remove the baseline files from the make dist file list.

https://github.com/google/protobuf/pull/1762 remove the files, but I forgot to
update Makefile.am to remove them.

Modify csharp README since there are now two NuGet packages

Remove unnecessary reflection call

This is the only call to TypeExtensions.IsValueType, so we can remove
that method, making the whole type conditionally compiled out for .NET 3.5

Drop the performace baselines.

We weren't really using them, and the nested path causes checkout problems
on windows.

Don't #import the .m files.

Change placement of DebuggerNonUserCodeAttribute

Make sure also Solaris x86 gets PATH_MAX

This does not affect the generated code.
If we decide we want to apply attributes to generated types, we should start by
just reverting this change.

Fix problems detected when integrating the code to our internal repo.

As bazel folks are looking at getting auto generation of module maps going and
the importing of sources files causes issues there.  We were only do it to
hack around some of the apple linker behaviors around objc classes and
categories, but even that isn't complete and CocoaPods was already doing -ObjC,
and developers not using pods could have still needed it to ensure everything
was linked anyways; so drop the hack of importing sources.

Fix spelling

Fixed failing JS tests

A couple of small tweaks were needed to fix test failures that were
inadvertently introduced in the last down integration. I also had to add
the map.js file which was missing.

add nullable qualifier to return types that can be nil, to support Swift 2 try-catch syntax

Add the `nullable` qualifier to return types of Objective-C methods that
can return a nil due to errors. This change makes these methods
compatible with the Swift 2 try-catch syntax.

I think this has caught everything.
I've left a stub for attributes to be applied to the types themselves, but we don't currently need anything.

Follow-up commit will include the changes to generated code itself.

Fixes #1671.

Add JsonParseOptions to ignore unknown fields

Fix some failing travis tests.