properly ignore coverage for this branch.

Though I still don't know how to come up with a test to cover it.

Author: ikirudennis

textile/core.py

@@ -725,7 +725,7 @@ def markStartOfLinks(self, text):
 
                         try:
                             possibility = possible_start_quotes.pop()
-                        except IndexError: # pragma: no branch
+                        except IndexError: # pragma: no cover
                             # If out of possible starting segments we back the
                             # last one from the linkparts array
                             linkparts.pop()