Improved the handling of matrices in serialization so that it's more reliable,

change was to use doubles for reading and writing matrices regardless of type of Matrix
being serialized.

Change does break backwards compatibility though, so code
path supporting original format has been left in for the
time being.  However, this code is not reliable enough and
is over complicated compared to the simplified handling.   Once
the new code has been bedded down for a while I'll remove this code block.

include/osgDB/InputStream

@@ -69,7 +69,6 @@ public:
     virtual ~InputStream();
     
     bool isBinary() const { return _in->isBinary(); }
-    bool getUseFloatMatrix() const { return _useFloatMatrix; }
     const osgDB::Options* getOptions() const { return _options.get(); }
     
     // Serialization related functions
@@ -161,7 +160,6 @@ protected:
     IdentifierMap _identifierMap;
     
     int _byteSwap;
-    bool _useFloatMatrix;
     bool _useSchemaData;
     bool _forceReadingImage;
     std::vector<std::string> _fields;