Cause MenuDeactivate event to be delivered when appropriate

This is achieved by moving the FireMenuDeactivate call to
MenuStrip.Dismiss and causing it to be called in a couple of places
where it ought to be.
X11: improve handling of WS_EX_TOPMOST

Currently, WS_EX_TOPMOST is handled by making the window transient-for
the root window.  I was unable to find any documentation that indicated
that this would have the desired effect.  Instead, use SetTopmost to
set _NET_WM_STATE to _NET_WM_STATE_ABOVE, per EWMH.

Also, use XMapRaised to raise topmost windows to the top of the stack
when mapped, as a last ditch effort to support window managers that
do not respect _NET_WM_STATE, such as xmonad.

This fixes an issue I encountered when running a winforms application
in xmonad, whereby drop down menus would fail to re-open if windows
had been re-arranged after the menu was first opened (in reality,
the menu was hiding behind the form).
Ignore the gdiplus dllmap on Windows.
Fix Bug 4811, xbuild should find xml documentation
[System] Don't overwrite custom Connection header on HttpWebRequest
[System] Add crude (for now) socket stealing of an HttpWebRequest.

HttpWebRequest is a very tricky piece of code when it comes to its socket, this patch is more like a hack to get something working out of it but it's definitely not the best option.
[System] Implement a first pass of ClientWebSocket.
[runtime] Make a marshalling test more robust.
[runtime] Add more logging to a test which fails on wrench.
Fix the test added by e682eceec3066a26afff333a7c1eb0e977ce7caa.
Implements parsing of multi value User-Agent string. Fixes #8719
[runtime] Thread teardown race condition.  Fixes #13813.
Add another extension point to the runtime.
[System]: WebRequest.GetSystemProxy(): Return custom proxy for monodroid.

On ICS and newer, we can use Java.Net.ProxySelector, which supports
per-access point proxy settings.  Fixes #12640.
[sdb] Add support for invoking interface methods. Fixes #14503.
[runtime] Fix the mingw build by defining InterlockedCompareExchange64 () which is missing from mingw's winbase.h.
Don't print empty detailed assert message
[runtime] Force the usage of --host=i686-pc-mingw32 when running configure on windows.
[Scripts] Fix a Shebang in mono-test-install for freeBSD
Fixes parallel enumerable index counter. Fixes #14515