Added osg::Image::set/getWriteHint() that allows images themselves to control how

they are written to disk, either inline or as an external file.  Added support for
this in the .ive plugin.  Default of WriteHint is NO_PREFERNCE, in which case it's
up to the reader/writer to decide.

include/osg/Image

@@ -79,6 +79,15 @@ class OSG_EXPORT Image : public Object
         void setFileName(const std::string& fileName);
         inline const std::string& getFileName() const { return _fileName; }
         
+        enum WriteHint {
+            NO_PREFERENCE,
+            STORE_INLINE,
+            EXTERNAL_FILE
+        };
+        
+        void setWriteHint(WriteHint writeHint) { _writeHint = writeHint; }
+        WriteHint getWriteHint() const { return _writeHint; }
+        
         enum AllocationMode {
             NO_DELETE,
             USE_NEW_DELETE,
@@ -307,6 +316,8 @@ class OSG_EXPORT Image : public Object
         Image& operator = (const Image&) { return *this; }
 
         std::string _fileName;
+        WriteHint   _writeHint;
+
 
         Origin _origin;