Added support for .sgi alias extension to the .rgb plugin.

src/osgDB/Registry.cpp

@@ -59,7 +59,7 @@ Registry::Registry()
     initFilePathLists();
 
     // register file extension alias.
-    addFileExtensionAlias("sgi", "rgb");
+    addFileExtensionAlias("sgi",  "rgb");
     addFileExtensionAlias("rgba", "rgb");
     addFileExtensionAlias("int",  "rgb");
     addFileExtensionAlias("inta", "rgb");

src/osgPlugins/rgb/ReaderWriterRGB.cpp

@@ -297,6 +297,7 @@ class ReaderWriterRGB : public osgDB::ReaderWriter
         virtual bool acceptsExtension(const std::string& extension)
         {
             return osgDB::equalCaseInsensitive(extension,"rgb") ||
+                osgDB::equalCaseInsensitive(extension,"sgi") ||
                 osgDB::equalCaseInsensitive(extension,"rgba") ||
                 osgDB::equalCaseInsensitive(extension,"int") || 
                 osgDB::equalCaseInsensitive(extension,"inta") ||