skip crash tests by default

IPython/testing/iptest.py

@@ -476,6 +476,8 b' def run_iptest():'
                         # setuptools devs refuse to fix this problem!
                         '--exe',
                         ]
+    if '-a' not in argv and '-A' not in argv:
+        argv = argv + ['-a', '!crash']
 
     if nose.__version__ >= '0.11':
         # I don't fully understand why we need this one, but depending on what