In Preparation for VS2019 (now in Preview)

In Preparation for VS2019 (now in Preview)

VS2017 version 15.9.3 has begun issuing the following warning for all compilations using the
v141_xp toolset (i.e. all of WinMerge).  VS2019 (now in Preview 1) still optionally provides the
v141_xp toolset (it has to be installed by the VS Installer); it too generates the same warning.

    " ... PlatformToolsets\v141_xp\Toolset.targets(39,5):
    warning MSB8051: Support for targeting Windows XP is deprecated and will not be present in
    future releases of Visual Studio. Please see https://go.microsoft.com/fwlink/?linkid=2023588
    for more information."

* The temporary way to suppress this warning is to set the <XPDeprecationWarning> property
to `false` for each build configuration in each `*.vs2017.vcxproj` file.  There is no Solution or
Project "wizard" interface to do this;  these property changes were inserted manually.  This
suppression seems to work for both VS2017 and VS2019

* It appears that at some point VS2019 will stop supporting Win XP ... but everything is still
functional at this point