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.
STYLE: create a new base class cmCoreTryCompile, from which
cmTryCompileCommand and cmTryRunCommand are derived, so there are no public
static functions with lots of arguments anymore
Alex