demandimport: add '_ctypes.pointer' to ignore list on PyPy

The pointer module is shadowed by a subsequent import. Our demand importer
can't handle this because both sub modules and attributes live in the same
namespace.

https://bitbucket.org/pypy/pypy/src/release-5.0.1/lib_pypy/_ctypes/__init__.py#__init__.py-5

mercurial/demandimport.py

@@ -287,6 +287,12 b' ignore = ['
     'distutils.msvc9compiler',
     ]
 
+if _pypy:
+    ignore.extend([
+        # _ctypes.pointer is shadowed by "from ... import pointer" (PyPy 5)
+        '_ctypes.pointer',
+    ])
+
 def isenabled():
     return builtins.__import__ == _demandimport