core:Text handle unicode names for fonts

Testing with the following code::

```
#-*- coding: utf-8 -*-
from kivy.app import App
from kivy.lang import Builder

root = Builder.load_string('''
Label:
    #text: 'सपषृ'
    font_size: '72sp'
    #font_name: 'सदगुरु.ttf'
''')

class TestApp(App):

    def build(self):
        root.text = u'सपषृ'
        root.font_name = b'सदगुरु.ttf'
        return root

if __name__ == '__main__':
    TestApp().run()
```
code and font file here https://docs.google.com/file/d/0B1WO07-OL50_VVVMejJDR2k1YUE/edit