Fixed NullReferenceExcepton in Socket.Connect for non-IP endpoints

Socket.Connect(EndPoint) throws a NullReferenceException when connecting to non-IP (eg Unix) endpoints in Dgram mode.
Added fix for Bug 20869
[dist] Do not include .git link files in dist tarball

Recent versions of Git co-host submodule GIT_DIRs in <root-project>/.git/
by default, and write their relative path into <subproject>/.git,
which is a regular file:

    $ ls -l external/cecil/.git
    -rw-r--r-- 1 foo  bar  42 Jun 16 12:50 external/cecil/.git
    $ cat external/cecil/.git
    gitdir: ../../.git/modules/external/cecil

Relax the expression in Makefile.am to also delete these (broken)
"symlinks" when preparing a distribution tarball.
Merge pull request #1140 from kitsilanosoftware/no-gitlink-in-dist

[dist] Do not include .git link files in dist tarball
Allocate the finalizable object in finalizer-exception.cs in another thread to make it less likely that it is retained. Fixes finalizer-exception.exe on 64 bit osx+llvm.
[mcs] Re-add obsolete reporting for enumerators removed in 6643bc119cbe1e94b5634e6452dd6eb40c7681c7
[mcs] Emit correct token for inherited nested non-generic types from unbound types
[mcs] Emit valid code for exception filter using constrained type parameter
[mcs] Add missing lock expression flow analysis
[tools] Fixed mono-shlib-cop test

MONO_PATH was missing when running the tests.

Use "libMonoPosixHelper.so" in local directory when checking if DllImport of a development library generates a warning (libglib2.0-dev might not be installed, but libMonoPosixHelper is always built with mono)
Fix the marshal7.cs test, longs can be aligned to 4 bytes on 32 bit linux, and the runtime no longer aligns structure sizes to 8 bytes. Fixes #20788.
Merge pull request #1141 from akoeplinger/fix-mono-shlib-cop

[tools] Fixed mono-shlib-cop test
[runtime] Make WaitForPendingFinalizers () really wait for the finalizers added by a previous GC. Fixes #20503.
[tests] gc-descriptors: Only copy file in case of VPATH build

Instead of ignoring the cp error when copying over the same file in non-VPATH builds.
Merge pull request #1127 from oleg-st/master

Added fix for Bug 20869
Merge pull request #1143 from akoeplinger/fix-gc-descriptor-error

[tests] gc-descriptors: Only copy file in case of VPATH build
[mini] Simplify the way the JIT emits atomic opcodes.

* MONO_ARCH_HAVE_ATOMIC_* macros have been removed.
* Backends now report whether they support atomic opcodes via
  the mono_arch_opcode_supported () function.
* The default implementation of mono_arch_opcode_supported ()
  has been removed as almost all backends need to define one
  anyway.
* All old atomic_add_* opcodes have been removed. These were no
  longer being used but some backends still had code for them.
* atomic_add_new_* opcodes have been renamed to atomic_add_* as
  they are now the only atomic add opcodes.
* Itanium-specific atomic_add_imm_* opcodes have been moved to
  the __ia64__ section of mini-ops.h.
* Comments have been added to mini-ops.h explaining the precise
  semantics of the atomic opcodes.

The net result of this change is a simpler backend interface at
the cost of a slightly bigger binary.
[ppc] Clean up atomic opcodes.

* Support atomic_add_i4 on ppc32 in addition to ppc64.
* Make the atomic_add_* code more in line with the atomic_cas_* code.
[corlib] Re-enable TaskContinuationChainLeak test.

This is hopefully fixed after a57fb5b.
[runtime] Fix the android build.