[CMake] Spurious errors with Visual Studio generator

[Dan Kegel]

I'm getting spurious errors like

error opening key: Software\Microsoft\VisualStudio\10.0\vsmacros\OtherProjects7
error opening key:
Software\Microsoft\VisualStudio\10.0\vsmacros\RecordingProject7

with cmake 3.0.1 and Visual Studio 2010 (but not 2013).
This was reported once before,
http://www.cmake.org/pipermail/cmake/2010-February/035321.html

This is on a buildbot that's been in use for some time, with
only one user.  Only very occasionally is the IDE used; mostly
it's doing unattended builds.

The errors don't seem to cause any problem, but they sure are confusing
when trying to track down unrelated errors.