Add FilenameMunger class to processing, with tests.

Munging filenames is something all media type processors want to be able to
do, so I'm refactoring it out into a nice bite-sized class.

mediagoblin/tests/test_processing.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+
+from nose.tools import assert_equal, assert_true, assert_false
+
+from mediagoblin import processing
+
+class TestProcessing(object):
+    def run_munge(self, input, format, output=None):
+        munger = processing.FilenameMunger(input)
+        result = munger.munge(format)
+        if output is None:
+            return result
+        assert_equal(output, result)
+        
+    def test_easy_filename_munge(self):
+        self.run_munge('/home/user/foo.TXT', '{basename}bar{ext}', 'foobar.txt')
+
+    def test_long_filename_munge(self):
+        self.run_munge('{0}.png'.format('A' * 300), 'image-{basename}{ext}',
+                       'image-{0}.png'.format('A' * 245))