PERF: add ix scalar get benchmark
@y-p question about test_perf. I just added a benchmark in the vb_suite. Which of course didn't exist if I want to compare to a commit in say 0.10.1. How do I make this work?

```
*** Running benchmarks for baseline [8a79d0d]
Running 6 benchmarks for revision 8a79d0d
indexing_frame_get_value_ix
indexing_dataframe_boolean
indexing_dataframe_boolean_rows
indexing_dataframe_boolean_rows_object
indexing_panel_subset
indexing_frame_get_value
```

```
./test_perf.sh -b 8a79d0d3b4d3992a955066ed6085a732eb0041c6 -t 7b2eaa4983162511868ce4ef7e567c97cae89fe3 -r indexing

-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------
indexing_dataframe_boolean                   |   8.2850 |  36.8630 |   0.2248 |
indexing_dataframe_boolean_rows_object       |   0.4253 |   0.3800 |   1.1192 |
indexing_panel_subset                        |   0.4750 |   0.4147 |   1.1455 |
indexing_dataframe_boolean_rows              |   0.2220 |   0.1824 |   1.2170 |
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------

Ratio < 1.0 means the target commit is faster then the baseline.
Seed used: 1234

Target [7b2eaa4] : Merge pull request #4207 from jreback/indexing_perf
Base   [8a79d0d] : RLS: Version 0.10.1

```
 ```
git checkout v0.10.1
git checkout upstream/master vb_suite # bring in vb_suite from the future
```

then run test_perf and save the results to a pickled df. The vbenches are reasonably decoupled from the rest of the pandas codebase.

I added the option to compare two pickle files a while back, I think.
 @y-p that worked...thanks

I didn't see the compare option...but for this case didn't matter ayhow....
