Refactored 'Constant' to 'NCConstant' in ncgen/ to avoid
reserved word collision on Windows.

Added tst_ncgen4_classic.sh to CMake-based builds.



git-svn-id: https://sub.unidata.ucar.edu/netcdf/trunk@3303 2e3060e4-1ed8-cf1f-9cc2-9586e844a556