missing_value & _FillValue bug fix

[ros]

Section 2.5.1 states that the missing_value and _FillValue attributes must be the same type as the variable to which they are attached. The CF checker throws a python error if these attributes are of type string/char.

The following generates the error, but is actually valid.

char variable(time) ;
    variable:standard_name = "surface_temperature" ;
    variable:_FillValue = "M" ;
    variable:missing_value = "M" ;

[ros]

Fixed in revision [55]

Caused by the attribute type of missing_value and _FillValue being specified as Numeric (N). Changed this to (D) to indicate it must match the type of the variable to which the attribute is attached.

The separate type checks run in chk_FillValue() have been removed as they are now covered by the changes made to chkAttribute() as a result of the introduction of the attribute type (D).

The attribute types table in Appendix A of the CF Conventions Document will need to be updated accordingly. A new ticket proposing changes to the Conventions/Conformance? document will be raised.

[ros]

CF Conventions Document updated as detailed in ticket #23