Added NC_HAVE_RENAME_GRP as per Charlie Zender's request:

https://www.unidata.ucar.edu/esupport/staff/index.php?_m=tickets&_a=viewticket&ticketid=22442

Updated configure.ac, CMakeLists.txt to reflect the upcoming 4.3.1-rc1
release.

Added notes to RELEASE_NOTES and RELEASE_NOTES.md


git-svn-id: https://sub.unidata.ucar.edu/netcdf/trunk@3366 2e3060e4-1ed8-cf1f-9cc2-9586e844a556