The problem with the previous approach and building inside Visual Studio was that makefile.vc in both Tcl and Tk first checks for one of "MSDEVDIR", "MSVCDIR", "VCINSTALLDIR", "MSSDK" or "WINDOWSSDKDIR" being set, which Visual Studio doesn't set.  That issue could have been fixed basically the same way I fixed it in the new approach (set "MSDEVDIR" to a dummy value, probably in build_tkinter.py), but the new approach strikes me as being simpler and cleaner.  Not to mention that without the dependency python.vcxproj, tcl/tk/tix can be built in parallel with other projects (like pythoncore, the longest-running Python project) using the msbuild /m switch.

I welcome having more eyes on it :).  I definitely won't be committing before 3.4.0 final (scheduled for the 16th), and it may be a week or better after that before I have good opportunity.