Garbage Collector
Many changes went into our GC implementation. We added long links support to our traditional Boehm collector. As for SGen, it is finally a true concurrent GC, with cementing support. We also fixed several bugs, such as #9928 pointer free deadlock problem and bugs in mono_gc_weak_link_get.
Async
Rewrite of async StreamReader/StreamWritter operations to not fail on subsequent async call. Fixes #9761
ASP.NET
Updated encoding support.
Some minor bug fixes.
Other improvements
New MONO_DISABLE_SHARED_AREA environment variable lets you turn of the use of shared memory in Mono (used by performance counters and optionally by the io-layer).
Updated EntityFramework version that ships with Mono.
Support for ConnectionLifetime parameter in SqlClient (contributed by 7digital).
Fixed C# Evaluator Terse reader with loops
Don't report user operator error during probing user conversions. Fixes #10170.
Add explicit interface GetType implementation to avoid object::GetType become proxy. (C# compiler fix)
Implement use of __refvalue as an lvalue. Fixes #10034.
Packaging
We no longer install a /usr/bin/pkg-config on OSX, to stop clashing with Homebrew.