tests: disable test of buffer overflow in parsers.c if --pure

It fails with AttributeError and there's no benefit to make it runnable
with pure Python code.

tests/hghave.py

@@ -376,3 +376,7 b' def has_absimport():'
 @check("py3k", "running with Python 3.x")
 def has_py3k():
     return 3 == sys.version_info[0]
+
+@check("pure", "running with pure Python code")
+def has_pure():
+    return os.environ.get("HGTEST_RUN_TESTS_PURE") == "--pure"

tests/test-parseindex.t

@@ -62,6 +62,8 b' We approximate that by reducing the read'
 
 Test corrupted p1/p2 fields that could cause SEGV at parsers.c:
 
+#if no-pure
+
   $ mkdir invalidparent
   $ cd invalidparent
 
@@ -118,3 +120,5 b' Test corrupted p1/p2 fields that could c'
   find_deepest: parent out of range
 
   $ cd ..
+
+#endif