Exposed more supports tests

Extra feature detection tests, to know what to load when using library

e.g. 
If no compressed texture support, load regular textures etc
If no float texture support, do multi pass rendering and pack float into rgba
If no dervitives do something else...

src/renderers/WebGLRenderer.js

@@ -263,6 +263,24 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	};
 
+	this.supportsFloatTextures = function () {
+
+		return _glExtensionTextureFloat;
+
+	};
+	
+	this.supportsStandardDerivatives = function () {
+
+		return _glExtensionStandardDerivatives;
+
+	};
+	
+	this.supportsCompressedTextureS3TC = function () {
+
+		return _glExtensionCompressedTextureS3TC;
+
+	};
+	
 	this.getMaxAnisotropy  = function () {
 
 		return _maxAnisotropy;