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.
The command argument parser code is generated by bison. This change
restores some fixes previously applied to the generated output that were
destroyed by regenerating the parser source. This time the fixes have
been put in the input file so regenerating the parser will not destroy
them again.
The $ENV{VAR} syntax permits access to environment variables. This
teaches CMake to recognize most characters in the VAR name since some
environments may have variables with non-C-identifier characters.
