[NCF-273]/HZY-708311

Add a new function called nc_inq_format_extended that
returns more detailed format information (vis-a-vis
nc_inq_format) about an open dataset.

Note that the netcdf API will present the file as if it had
the format specified by nc_inq_format.  The true file
format, however, may not even be a netcdf file; it might be
DAP, HDF4, or PNETCDF, for example. This function returns
that true file type.  It also returns the effective mode for
the file.

signature: nc_inq_format_extended(int ncid, int* formatp, int* modep)
where
* ncid is the NetCDF ID from a previous call to nc_open() or
  nc_create().
* formatp is a pointer to a location for returned true format.
* modep is a pointer to a location for returned mode flags.

Refer to the actual list in the file netcdf.h to see the
currently defined set.

Also added test cases (tst_formatx*).