Unicode in filenames issue with generate_css_name

[rickybrent]

generate_css_name runs into a problem when checking the filename to see if it contains the css_pseudo_class_separator if the filename is in unicode.

I've attached my error log -- the "problem file" was "Flügel Tiara_9.png"

---

Version: 0.11.1
Python: 2.7.6 (default, Jun 22 2015, 17:58:13)
[GCC 4.8.2]
PIL version: 1.1.7
Platform: Linux-3.13.0-77-generic-x86_64-with-Ubuntu-14.04-trusty
Config: {'css_dir': '/home/ricky/dumps/sprites', 'less_dir': False, 'force': False, 'json_dir': False, 'crop': False, 'less_template': None, 'css_url': u'', 'global_template': None, 'css_namespace': u'sprite', 'html_dir': False, 'css_cachebuster': False, 'recursive': False, 'scss_template': None, 'css_pseudo_class_separator': u'__', 'enabled_formats': ['img', 'css'], 'generate_css': True, 'source': '/home/ricky/dumps/itempanel_icons', 'optipng': False, 'follow_links': False, 'imagemagick': False, 'each_template': None, 'json_format': u'array', 'watch': False, 'css_sprite_namespace': u'{sprite_name}', 'padding': u'0', 'ratio_template': None, 'ratios': u'1', 'caat_dir': False, 'optipngpath': None, 'css_cachebuster_only_sprites': False, 'scss_dir': False, 'generate_image': True, 'cocos2d_dir': False, 'imagemagickpath': None, 'algorithm': u'square', 'css_cachebuster_filename': False, 'img_dir': '/home/ricky/dumps/sprites', 'png8': False, 'quiet': False, 'project': False, 'css_separator': u'-', 'algorithm_ordering': u'maxside', 'debug': False, 'output': '/home/ricky/dumps/sprites', 'margin': u'0', 'css_template': None, 'ignore_filename_paddings': False}
Args: ['/usr/local/bin/glue', 'itempanel_icons', 'sprites']

Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/glue/bin.py", line 235, in main
manager.process()
File "/usr/local/lib/python2.7/dist-packages/glue/managers/base.py", line 14, in process
self.save()
File "/usr/local/lib/python2.7/dist-packages/glue/managers/base.py", line 42, in save
format.validate()
File "/usr/local/lib/python2.7/dist-packages/glue/formats/css.py", line 142, in validate
class_names = [':'.join(self.generate_css_name(i.filename)) for i in self.sprite.images]
File "/usr/local/lib/python2.7/dist-packages/glue/formats/css.py", line 211, in generate_css_name
if css_pseudo_class_separator in filename:
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 2: ordinal not in range(128)

[rickybrent]

Noticed this is a duplicate of #203