replace C comment '//' as when compile with -ansi, it can fail

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1752 c368ceb8-fd28-0410-a457-e46ee1d7cd4a
add note of recent changes

git-svn-id: https://svn.mcs.anl.gov/repos/parallel-netcdf/trunk@1753 c368ceb8-fd28-0410-a457-e46ee1d7cd4a