COMPAT: 32-bit compat fixes mainly in testing
closes #13566

this was a PITA 

cc @jorisvandenbossche 
cc @sinhrks 
cc @gfyoung 

passing on 32-bit linux & windows & travis.
 @jreback : any reason why we don't test 32-bit for PR's?  Our parent library `numpy` has at least one machine for 32-bit testing as you can see <a href="https://github.com/numpy/numpy/blob/master/.travis.yml#L40">here</a>.
 oh didn't know you could set it up that way 

sure u want to add another build (under the bottom section - go for it)
 There's a little bit more that happens behind the scenes, but I just wanted to throw that out there.  I can certainly take a look.
 What is the reason `searchsorted` has to return platform int?
 Alas, adding a 32-bit config is way more complicated than I imagined (I thought perhaps Ctrl+P from `numpy` might suffice, but alas, that doesn't even work).  So tabling that idea for now.
 32-bit linux

```
In [12]: arr = np.array([0,1,2])

In [13]: arr.dtype
Out[13]: dtype('int32')

In [14]: arr.searchsorted(arr).dtype
Out[14]: dtype('int32')
```

64-bit windows

```
In [15]: arr = np.array([0,1,2])

In [16]: arr.dtype
Out[16]: dtype('int32')

In [17]: arr.searchsorted(arr)
Out[17]: array([0, 1, 2], dtype=int64)
```

64-bit all around / OSX

```
In [1]: arr = np.array([0,1,2])

In [2]: arr.searchsorted(arr)
Out[2]: array([0, 1, 2])

In [3]: arr.searchsorted(arr).dtype
Out[3]: dtype('int64')

In [4]: arr.dtype
Out[4]: dtype('int64')
```

So the issue is that on 64-bit we have integers defaults to 64-bit upon construction, and indexing routines (e.g. `.searchsorted` and `.take` are also 64-bit)
On 32-bit these are both 32-bit
on windows indexing are 64-bit but 32-bit for integer defaults (this is because windows use `long long` for pointers, but `long` for integer)

Note that this is NOT an API change, rather a regression to 0.18.1 (so putting it back where it was). Will update soon.

I think somewhere we are doing a forced conversion (in `.searchsorted`) but should not be.
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13584?src=pr) is **84.31%**

> Merging [#13584](https://codecov.io/gh/pydata/pandas/pull/13584?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will not change coverage

``` diff
@@             master     #13584   diff @@
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  Files           138        138          
  Lines         51155      51155          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
  Hits          43130      43130          
  Misses         8025       8025          
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last updated by [2655dae...b624ce0](https://codecov.io/gh/pydata/pandas/compare/2655daef1b7346feabd00d4d40910a80386d0812...b624ce09dceef66897702a9f3534f6959f179a75?src=pr)
