update to newest VS2017 Release 15.5

[GreyMerlin]

Three small commits to update to the newest VS2017 15.5 Release (November 2017)

• VS2017 - 15.5.0 kludge for GTest UnitTests
• Fix Boost's checking for new VS2017 Version 15.5.0
• VS2017 15.5.0 updated version in .sln file

VS2017 - 15.5.0 kludge for GTest UnitTests

• Using the latest (and just released) version 15.5.0 of VS2017 introduces the following error (about 2400 times !) into the UnitTests project ...

"error C4996: 'std::tr1': warning STL4002: The non-Standard std::tr1 namespace and TR1-only machinery are deprecated and will be REMOVED. You can define _SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING to acknowledge that you have received this warning. "

• MSDN claims that this is a C++17 language standards issue, but I was not able to solve this problem by specifying the use of the C++14 standard language (the Properties control for this is likewise a new
  feature of version 15.5.0)
  See... https://docs.microsoft.com/en-us/cpp/cpp-conformance-improvements-2017

• The only simple, short-term solution that I could come up with was to simply follow the suggestion of defining the _SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING token as given above.

• Even though this problem has been discussed in the GoogleTest GitHub forum since at least 6 June, the underlying problem remains unresolved at this hour (well, by late 6 Dec anyway)...
  See... googletest uses std::tr1 which will be deprecated in VS 2017 google/googletest#1111
  See... Compilation error (Gtest + Library using TR1) google/googletest#1320
  See... fix for VS2017 Preview deprecation of ::tr1::tuple google/googletest#1311

• I will assume that the GoogleTest resolution of this problem will require WinMerge to adopt the newest GoogleTest framework (which is likely a good idea anyway). I will keep an eye on their progress and resolution and advise accordingly.

• In the meantime, this kludge allows WinMerge's UnitTests project to compile and execute correctly.

Fix Boost's checking for new VS2017 Version 15.5.0

• Update 5 (dated Oct 2017) changes _MSC_VER to 1912.
  See... https://blogs.msdn.microsoft.com/vcblog/2017/11/15/msvc-conformance-improvements-in-visual-studio-2017-version-15-5/

• This causes lots of compilation messages (neither Errors nor Warnings) with the text Unknown compiler version - please run the configure tests and report the results. I have not reported this new issue to Boost.org (they will eventually catch up without my help)

• This tiny patch will prevent those compilation messages until a newer version of Boost becomes available and WinMerge chooses to adopt it.

• Since this has been a hard message to find twice now (previously with VS2017 15.3.0), I have added a new filter Boost to the Solution Explorer, containing a very small selection of boost configuration
  files. Boost itself is too large to include either completely, or even the reasonably small subset of boost files that WinMerge uses.

• Mimic changes also for VS2015 to add the Boost filter to the Solution Explorer, even though this problem will never occur with VS2015

VS2017 15.5.0 updated version in .sln file

• A simple auto-update of the WinMerge.vs2017.sln file

[GreyMerlin]

Just an FYI ... VS2017 version 15.5.1 was released today (8 Dec). These three commits remain relevant, i.e. nothing in this new VS2017 changed anything related to these issues.

[sdottaka]

Thank you!