bug fix: misplace define check PNC_MALLOC_TRACE

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1788 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
new error code, NC_EINVAL_CMODE, for when NC_64BIT_OFFSET and NC_64BIT_DATA are set for create mode. Add test program test/testcases/modes.c

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1789 c368ceb8-fd28-0410-a457-e46ee1d7cd4a