interhg: escape backslashes in docstring

hgext/interhg.py

@@ -22,9 +22,9 To enable this extension, add the follow
 A few example patterns (link to bug tracking, etc.):
 
   [interhg]
-  issues = s!issue(\d+)!<a href="http://bts/issue\1">issue\1</a>!
-  bugzilla = s!((?:bug|b=|(?=#?\d{4,}))(?:\s*#?)(\d+))!<a..=\2">\1</a>!i
-  boldify = s!(^|\s)#(\d+)\b! <b>#\2</b>!
+  issues = s!issue(\\d+)!<a href="http://bts/issue\\1">issue\\1</a>!
+  bugzilla = s!((?:bug|b=|(?=#?\\d{4,}))(?:\\s*#?)(\\d+))!<a..=\\2">\\1</a>!i
+  boldify = s!(^|\\s)#(\\d+)\\b! <b>#\\2</b>!
 '''
 
 import re