Add support for value types to mono_object_to_string

The current mono_object_to_string implementation does not support value types. This patch adds support by unboxing value types prior to calling mono_runtime_invoke.
Fixed xamarin bug #13708: routing constraints should be trated as 'convertible to string' in order to be compat with MS.NET
[ThreadPool] Allow heavier initialization when using --server flag

Create on demand up to min_threads to avoid startup penalty, avoiding
throttling of threadpool worker thread creation (for now, using
a --server flag) at initialization.

When throttling happens, operations such as parallel https requests were
slowed down significantly due to all of the threads created in order
to complete the SSL operations.

Based on @kamalaboulhosn's patch (https://github.com/mono/mono/pull/640/files)
Boilerplate implementation of Charting

Implemented enough of
System.Windows.Forms.DataVisualization.Charting to get two pieces of
software to compile: the charting examples from MSDN and the windows OSS
EVEMon.

This patch contains the majority of properties defined, and many methods
stubbed - I have avoided implementing any functionality in this patch.

All this work is under the MIT Licence.
fix up some properties per mono coding guidelines
Enable MONO_ARCH_HAS_MONO_CONTEXT on mingw.
Clean up the win32 lmf code by using a separate variable to hold the jit_tls tls offset. Fix warnings.
Fix skipping of disabled runtime tests on windows.
Avoid infinite logfiles if the test-process-exit test fails to terminate.
Get rid of the annoying 'PLATFORM is not defined.' message on every build.
Fixed System.Text.Decoder.GetChars(byte*,int,char*,int,bool) to copy output into the char* buffer.
Fixed build breakage from my previous commit
Improved exception handling with vectored exception handling.
Now a native debugger can be used with soft debugger running without triggering any exception. Code provided by Jonathan Chambers:

* https://github.com/Unity-Technologies/mono/commit/e9f9f7170914c5caaff3e95e09f6f58ecced2a10
* https://github.com/Unity-Technologies/mono/commit/4c2e1db60ccb38e792545d595d85b12ff309a919
* https://github.com/Unity-Technologies/mono/commit/bd7e534aa7da49b89787b8c1b40e165a34c0e960
* https://github.com/Unity-Technologies/mono/commit/b885251a83969d243deabc56bb3d1495d4a971dc

From:

https://github.com/mono/mono/pull/724
Fixed MSVC build, ported to Visual Studio 2012.

From:

https://github.com/mono/mono/pull/724
Fixed incorrect pointer arithmetic on SGen for MSVC.

From:
https://github.com/mono/mono/pull/724
Fixed SGen build for MSVC

From:
https://github.com/mono/mono/pull/724
Merge pull request #708 from spicypixel/hotfix/mono-object-to-string

Add support for value types to mono_object_to_string
fix properties per mono guidelines
[aot] Align the static linking symbol.
[linker] Small string optimizations to avoid culture aware code paths