re: https://github.com/Unidata/netcdf-c/issues/1154
Inadvertently, the behavior of NC_DISKLESS with nc_create() was
changed in release 4.6.1. Previously, the NC_WRITE flag needed
to be explicitly used with NC_DISKLESS in order to cause the
created file to be persisted to disk.
Additional analyis indicated that the current NC_DISKLESS
implementation was seriously flawed.
This PR attempts to clean up and regularize the situation with
respect to NC_DISKLESS control. One important aspect of diskless
operation is that there are two different notions of write.
1. The file is read-write vs read-only when using the netcdf API.
2. The file is persisted or not to disk at nc_close().
Previously, these two were conflated. The rules now are
as follows.
1. NC_DISKLESS + NC_WRITE means that the file is read/write using the netcdf API
2. NC_DISKLESS + NC_PERSIST means that the file is persisted to a disk file at nc_close.
3. NC_DISKLESS + NC_PERSIST + NC_WRITE means both 1 and 2.
The NC_PERSIST flag is new and takes over the obsolete NC_MPIPOSIX flag.
NC_MPIPOSIX is still defined, but is now an alias for the NC_MPIIO flag.
It is also now the case that for netcdf-4, NC_DISKLESS is independent
of NC_INMEMORY and in fact it is an error to specify both flags
simultaneously.
Finally, the MMAP code was fixed to use NC_PERSIST as well.
Also marked MMAP as deprecated.
Also added a test case to test various combinations of NC_DISKLESS,
NC_PERSIST, and NC_WRITE.
This PR affects a number of files and especially test cases
that used NC_DISKLESS.
Misc. Unrelated fixes
1. fixed some warnings in ncdump/dumplib.c
