Fix obj texture parsing error when it contains texture option

<ol>
<li>Skip texture option to get texture image url correctly.
     According to http://en.wikipedia.org/wiki/Wavefront_.obj_file#Texture_options, Texture map statement can contains various texture option, for example:
	<ul>
        <li>map_Ka -o 1 1 1 some.png
	<li>map_Kd -clamp on some.png
        </ul>
    So we need to skip this option, just keep the last part which is the url of image, otherwise we will get a wrong url like "-clamp on some.png".  Here we also take a special case into account where url contains space:<br>
 	map_Kd -clamp on "url contains space.png"
<li> Add Clamp option support for obj texture mode.
   If  "-clamp on" is detected, we will set the texture mode to clamp.