COMPAT, TST: allow numpy array comparisons with complex dtypes
Traces back to bug in NumPy `v1.7.1` in which the `array_equivalent` method could not compare NumPy arrays with complicated dtypes. As `pandas` relies on this function to check NumPy array equality during testing, this commit adds a fallback method for doing so.

Closes #13388.

Didn't really think I needed a `whatsnew` in this case since this does seem rather internal to `pandas`.  If I do need one, not sure what I would write exactly.
 this needs perf testing, not sure how much that path is hit (so I don't think its an issue). but pls run them.
 @sinhrks 
 @jreback : Will quickly run benchmarks, but as this is just a compatibility issue (bug exists until `v.1.8.0` of `numpy`), this path will most certainly never be hit for the more recent versions.
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13392?src=pr) is **84.22%**

> Merging [#13392](https://codecov.io/gh/pydata/pandas/pull/13392?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #13392   diff @@
==========================================
  Files           138        138          
  Lines         50756      50763     +7   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          42756      42757     +1   
- Misses         8000       8006     +6   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [67b72e3...230616e](https://codecov.io/gh/pydata/pandas/compare/67b72e3cbbaeb89a5b9c780b2fe1c8d5eaa9c505...230616eebe7055c116b6822a2a294fd8571a6361)
 @jreback : Travis is passing on all machines again.  Ready to merge if there are no other concerns.
 benchmarks ok?
 No obvious changes in the benchmarks AFAICT and as expected.
 ty
