Update cg_is_cgns filetypes.

[brtnfld]

file_type: Type of CGNS file. This will typically be either CG_FILE_ADF or CG_FILE_HDF5 depending on the underlying file format. However, note that when built in 32-bit, there is also an option to create a Version 2.5 CGNS file by setting the file type to CG_FILE_ADF2.

Fix: Can also be CG_FILE_PHDF5

( Note: added missing CG_FILE_PHDF5 to the fortran constants). Added missing test for cg_is_cgns.