revise sunroutine equal, add equal2 for matched ityep and xtype APIs, and add nc_err_code_name
revise sunroutine equal, add equal2 for matched ityep and xtype APIs, and add nc_err_code_name

Unidata/netcdf-c,Unidata/netcdf-c,Unidata/netcdf-c,Unidata/netcdf-c