add new methods set and isfield, update get in tsg_nc class

@tsg_nc/get.m

 function result = get( self, varargin )
 
-% tsg_ncvar/get -- get structure of "tsg_ncvar" object.
+% tsg_nc/get -- get structure of "tsg_ncv" object.
 %
 % Input
 % -----
-% self   ........... instance of 'tsg_ncvar' object
-% key    ........... GF3 code
+% self   ........... instance of 'tsg_nc' object
+% key    ........... hashtable key
 % member ........... attribute member
 %
 % Output
 % ------
-% result ........... structure for the key (hastable)
+% result ........... structure for the key (hashtable)
+%
+% if key dosn't exist, return empty structure
 %
-% if key dosn't exist, return empty struct
-
 % $Id$
 
 % Test variable argument list
@@ -38,8 +38,10 @@ switch (nargin)
   % ----------------------------
   case 3
     % call method get for an hashtable object
+    % ---------------------------------------
     result = get(self, varargin{1});
     % test if third arg is a valid member of the struct in the hash
+    % -------------------------------------------------------------
     if ~isempty( find(strcmp(keys(self), varargin{1})) ) && ...
         isfield(result,varargin{2})
       result = result.(varargin{2});

@tsg_nc/isfield.m

+function bool = isfield( self, fieldname )
+
+% tsg_nc/get_fieldnames -- get internal structure fieldnames of "tsg_nc" object.
+%
+% Input
+% -----
+% self      ........... an instance of 'tsg_nc' object
+% fieldname ........... is field of internal structure ?
+%
+% Output
+% ------
+% bool       .......... true if fieldname is internal structure 
+
+% $Id: get_fieldnames.m 92 2008-01-09 11:10:40Z jgrelet $
+
+% get cell of keys inside object
+% ------------------------------
+c = get(self);
+if isempty(c)
+  warning('Empty object') ;
+else
+ % get structure for the first element
+ theStruc = get(self,c{1});
+ bool = isfield(theStruc, fieldname);
+end   
+    

@tsg_nc/set.m

-function self = set( self, varargin )
+function self = set( self, key, theStruct )
 
-% tsg_ncvar/set -- set new pair key/value for "tsg_ncvar" object.
+% tsg_nc/set -- set new pair key/value for "tsg_nc" object.
 %
-% not implemented yet
+% Input
+% -------
+% self      ........... instance of 'tsg_nc' object
+% key       ........... hashtable key
+% theStruct ........... hashtable structure
+%
+% Output
+% --------
+% self      ........... instance of updated 'tsg_nc' object
+%
+% $Id$
+
+% populate the internal hashtable
+% -------------------------------
+self.hashtable = put(self.hashtable, key, theStruct);
 
-% $Id£
+% update self.size
+% ----------------
+self.size = numel(keys(self.hashtable));