[System.Core] Bring .NET implementation of ReaderWriterLockSlim.
[System.Core] Removed no longer used files.
System.Core is now using .NET implementations of LockRecursionPolicy and ReaderWriterLockSlim.
[corlib] Fix needing write permission when reading registry values. Fixes #25106

ToKey() ignores the setting parameter when calling RegistryKey.OpenSubKey() and
thus always asks for write permission. If you try to read read-only keys (say
HKLM without admin rights) it will fail with a  SecurityException.
Merge pull request #1445 from meebey/registry_fix_unneeded_write_permission

[corlib] Fix needing write permission when reading registry values. Fixe...
[system] Fix soctec test to not block indefinitely
[system] Add test for #25137
[system] Replace System.Collections.Generic from reference sources
[MWF] Use Ctrl+PageUp/PageDown for Tab Navigation

In the Windows implementation of the TabControl, Ctrl+PageUp
navigates to the previous tab and Ctrl+PageDown navigates to the
next tab (with both wrapping around).  This change implements this
feature in the Mono implementation.

Change-Id: Ib940bd08d5ba641f05ed91c0e789e356e68f72bb
[mkbundle] fix execution for X.Android on Windows regarding dos2unix.

This fixes bug #25086 (Xamarin.Android). Details described there.

To fix the issue, we use #if XAMARIN_ANDROID to avoid that old cygwin-only
code path. (We are not sure if simply removing the old code still works,
so we don't remove that for now.)
[corlib] Remove duplicate FirstChanceExceptionEventArgs
Change 4.0 profile to metadata reference only profile
Added reference-assemblies submodule to fix the build
[corlib] Update SafeHandle dispose pattern to match .net. Fixes #25132
Use `git://...` instead of `git@...` for submodules.
Add DateTimeOffsetConverter to the default converters list.

This is the fix for https://bugzilla.xamarin.com/show_bug.cgi?id=25158

Current implementation does not contain the DateTimeOffsetConverter
in the list of default converters. This cause NotSupportedException
to be thrown when trying to serialize/deserialize DateTimeOffset
values to/from strings.

In .NET Framework implementation this class is added to such a list.
gmcs script is no longer installed.

The intention is to make build failures easy to spot instead of silently upgrading
target framework from 2 to 4 and then fail down the road on e.g type ambiguity
caused by new 4.0 framework types or methods
Revert "[build] Rework the buildver dep check."

This reverts commit a9f31e63db668955e2723796201d5c12dd146eae.

Revert this as it breaks make dist by having a source file depend on a generated file.
[runtime] Add another rule for the builder-sgen.h -> main-sgen.o dependency since apparently some versions of automake etc. generate a main-sgen.o file too.
[runtime] Remove the bug-438454.exe test, it tests behaviour which is by design.
[build] Print out the version of the bootstrap mcs if the profile check fails.