Thanks to "J Decker" on the CMake mailing list for pointing out
that one of the MSVC10_CRT_DIR settings was using "VC90" instead
of "VC100".

After fixing that, I added the code to generate a CMake warning
if one of the files we think is "required" does not exist.

Then, with VS10, there were several other problems that the
warning revealed:

 - MSVC10_REDIST_DIR needed more PATHS to be found correctly

 - the 64-bit directory is named "x64" now, not "amd64" as in
   previous VS versions

 - manifest files no longer exist as separate files in the
   redist subdirectories (they must be built-in as resources
   to the dlls...?)