BUG: Work-around a numpy regression affecting pandas.eval() with numexpr
numpy 1.7.0 erroneously raises IndexError instead of ValueError
from ndarray.item() when the array is not of length 1. This can be
seen as a failure of

```
computation.tests.test_eval.TestScope.test_global_scope
```

for the cases that engine='numexpr'.

Absorb the splatter from this regression by explicitly catching the
erroneous IndexError.

closes #5535.

weird that this is only on FreeBSD. any idea why?
 I don't think it is actually limited to FreeBSD. The affected code in numpy does not appear to be platform-dependent. I think that we just didn't see test failures, because as far as I can tell (pydata/pandas@5f4be91f, pydata/pandas@81739d9c) we've never actually encountered the affected version of numpy in the Travis-CI environment. The fix was backported to the 1.7.x maintenance branch prior to 1.7.1 (numpy/numpy@b84555ac).
 ahh that makes sense

but this is a fix for a version that is already fixed then in numpy,  why is it necessary to fix something that doesn't occur?
 It does occur if you're in an environment where 1.7.0 is present, like FreeBSD. Pandas may decide not to accept this patch as a matter of policy (e.g. we don't support numpy 1.7.0), in which case I could elect to apply the patch to the FreeBSD port. My aim, though, is to minimize the diff between the ported software and the published releases, so I would like to see this patch accepted.
 @neirbowj 

maybe I was not clear. Is the current numpy 1.7.0 patched? you said it was back ported? Or if you happend to have an 'older' numpy 1.7.0 then it (obviously) does not have the back port.
 @jreback 

Ah, I see now. No, numpy 1.7.0 does not have the fix and is broken. 1.7.1 is fixed and 1.8.0 is fixed.
 ahh..ok...then i don't see a problem with this (as it seems to work with 1.7.1/1.8 which we test)...

thanks for the fix
 can you add a release note referecing the issue?
 thanks for the fix!
 @neirbowj, are you in a position to put up a freebsd CI server / buildbot for us to track? 
 @y-p, That's a compelling possibility. I will look into it.
