add a pypy that is allowed to fail

.travis.yml

@@ -2,6 +2,7 @@ language: python
 python:
   - "2.7"
   - "2.6"
+  - "pypy"
 before_install:
   - sh -c set
   - git config --global user.email "travis-tahoe@tahoe-lafs.org"
@@ -23,3 +24,7 @@ notifications:
     template:
       - "%{repository}#%{build_number} [%{branch}: %{commit} by %{author}] %{message}"
       - "Changes: %{compare_url} | Details: %{build_url}"
+matrix:
+  allow_failures:
+    - python: "pypy"
+  fast_finish: true