Rename test #913 -> #957, comment

Make test for #957 reference correct bug. Add comment.

Previous commit closes #957.

spacy/language_data/tokenizer_exceptions.py

@@ -1,5 +1,7 @@
 from __future__ import unicode_literals
 
+# The use of this module turns out to be important, to avoid pathological
+# back-tracking. See Issue #957
 import regex
 
 # URL validation regex courtesy of: https://mathiasbynens.be/demo/url-regex
@@ -23,6 +25,8 @@ _URL_PATTERN = (
     # excludes reserved space >= 224.0.0.0
     # excludes network & broadcast addresses
     # (first & last IP address of each class)
+    # MH: Do we really need this? Seems excessive, and seems to have caused
+    # Issue #957
     r"(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])"
     r"(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}"
     r"(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))"