This converts the CMake license to a pure 3-clause OSI-approved BSD
License. We drop the previous license clause requiring modified
versions to be plainly marked. We also update the CMake copyright to
cover the full development time range.
This factors parts of the svn update implementation that are useful for
any globally-versioning vcs tool into cmCTestGlobalVC. It will allow
the code to be shared among the support classes for most vcs tools.