Switched to using git for Windows, rather than msysgit.

Using msysgit with git-annex is no longer supported.

At the same time, I'm updating the rsync.exe in my downloads repository
with the one from msys2.

Note that rsync is currently still being ldded and installed in Git/cmd/
like the other cygwin programs. The ldd fails and this failure is ignored.
It would be better to special case it to go in Git/usr/bin/, so that the
user can't run rsync in a dos prompt window, which doesn't work, as it needs
additional libs. However, as far as git-annex running rsync running ssh,
it works ok in this location.

Removed the ssh.cmd and ssh-keygen.cmd; these are not needed with git for
windows. Keeping them would let ssh be run manually from a dos prompt
window, but that's not really a goal.

doc/install/Windows.mdwn

@@ -1,7 +1,7 @@
 git-annex now does Windows!
 
-* First, [install msysgit](http://git-scm.com/downloads) (msysgit 1.9 is needed; the new "git for windows" does not currently work)  
-  _Be sure to tell the msysgit installer to add git to the PATH._
+* First, [install git for Windows](http://git-scm.com/downloads) (msysgit is no longer supported)  
+  _Be sure to tell the installer to add git to the PATH._
   That is, select "Use Git from the Windows Command Prompt"
 * Then, [install git-annex](https://downloads.kitenet.net/git-annex/windows/current/)
 
@@ -36,7 +36,7 @@ Once the prerequisites are installed, run:
 	build
 
 Note that git from Cygwin is able to clone git-annex's git repository;
-Msysgit cannot due to some characters in filenames.
+Regular git for Windows cannot due to some characters in filenames.
 
 (To build the git-annex installer, you also need to install the NullSoft
 installer system.)