Add pathological test for commonmark#285.

Author: jgm

test/pathological_tests.py

@@ -48,6 +48,9 @@
     "link openers and emph closers":
                  (("[ a_" * 50000),
                   re.compile("(\[ a_){50000}")),
+    "pattern [ (]( repeated":
+                 (("[ (](" * 80000),
+                  re.compile("(\[ \(\]\(){80000}")),
     "hard link/emph case":
                  ("**x [a*b**c*](d)",
                   re.compile("\\*\\*x <a href=\"d\">a<em>b\\*\\*c</em></a>")),