[Mono.Parallel] Removed broken Mono.Threading.Tasks code

The code in MonoTaskExtensions.cs relied on the internal method Execute(Action<Task>) in System.Threading.Tasks.Task which was removed in 0a66e60.
Added stress test to ConcurrentQueue.TryPeek.
The test checks that in some race condition the queue does not return null.
Changed TryPeek to handle race condition with Dequeue.
Dequeue sets the head.Value to its default. When TryPeek is interrupted in the process of retrieving the value some times Dequeue sets the value to its default. TryPeek now checks the head has not been changed before returning the value.
Fixed another 8080 test port

I missed that one in f396d37c5493455f0b7fe726b408d74ba1c8fb5f.
[ppc] Add missing `sync` instructions to atomic opcodes.

Note that lwarx and stwcx don't produce the necessary
load/store barrier that's needed to conform to the
`Interlocked` API.
ImageListStreamer generates winform resource files that work on Mono but fail on Microsoft.net
with exception System.InvalidOperationException: Loading of the ImageList did not succeed.
see bug https://bugzilla.xamarin.com/show_bug.cgi?id=3841 for detailed analysis
Expose full epoll_ctl functionality.

Now the user has access to all struct elements in EpollEvent when
using epoll_ctl. This is in particular very intersting when the
user wants to access the ptr field.

The user can use GCHandle.ToIntPtr to give the struct a GCHandle
and then handle the pointer later on when using epoll_wait.
Added dllmap for libgtk-x11 and libgdk-x11

Commit licensed under MIT/X11.
Merge pull request #1111 from akoeplinger/add-gtk-dllmap

Added dllmap for libgtk-x11 and libgdk-x11
Override registry storage with MONO_CURRENTUSER_REGISTRY_PATH

https://bugzilla.xamarin.com/show_bug.cgi?id=358
Merge pull request #1110 from tpokorra/FixImageListStreamerGeneratingValidResourcesForMSNet

Fixing ImageListStreamer generating winform resource files that work on MS.Net
Merge pull request #1014 from txdv/master

Expose full epoll_ctl functionality.
[ppc] Bump instruction sizes after 51c454f6b03b468273bb93db2aa9b76e330a7e57.
Merge pull request #1109 from adbre/iss358

Override registry storage with MONO_CURRENTUSER_REGISTRY_PATH
[System.ComponentModel] BindingList.ListChanged now attempts to provide a PropertyDescriptor when possible.
BindingList subscribes to PropertyChanged events of eligible contained objects. Iff the PropertyName provided is valid,
the list event's ListChangedEventArgs will also contain a PropertyDescriptor.

This is to match MS behavior.
[xbuild] Implements property functions using constructor syntax. Fixes #12999
Revert change that introduces a new undocumented environment variable
[xbuild] Parsing conditions with property references. Fixes #20634
Merge pull request #1074 from esdrubal/bug18421

Changed TryPeek to handle race condition with Dequeue.
Merge pull request #946 from akoeplinger/fix-mono-parallel

[Mono.Parallel] Removed broken Mono.Threading.Tasks code