Fix unrecognized selector issue in [NS.. SVGWhitespaceCharacterSet].

The issue can be found in [TouchVG](https://github.com/rhcad/touchvg)'s TestView-SVG project:
TestView-SVG[3660:60b] +[NSCharacterSet SVGWhitespaceCharacterSet]: unrecognized selector sent to class 0x39e43da0

The build and reappear way of [TouchVG](https://github.com/rhcad/TouchVG) (if you need it):
1. Check out TouchVG project containing [TouchVGCore](https://github.com/rhcad/TouchVGCore) and SVGKit submodules.
2. 'cd' to the 'ios' directory containing the file of 'build.sh', then type `./build.sh` to compile libraries.
3. Run TestView-SVG target.
4. Tap `GiPaintView SVG images` row, then the issue occurs.
`2014-02-05 00:50:33.655 TestView-SVG[40639:70b] +[NSCharacterSet SVGWhitespaceCharacterSet]: unrecognized selector sent to class 0x17f0ff0
2014-02-05 00:50:33.655 TestView-SVG[40639:70b] Fail to parse fonts.svg due to NSInvalidArgumentException`