PERF/TST: Figure out what's going on with vb_suite test result instability (`frame_reindex_*` in particular)
Example:

```
frame_reindex_axis1                  3.1934       2.0423       1.5636
frame_reindex_axis0                  1.4083       0.4687       3.0049

Target [b42175f] : dummy commit
Base   [da54321] : SCR: format tweaks to test_perf
```

with the following:

```
stephen@trantor:~/Projects/pandas$ git diff da54321 b42175f
diff --git a/TODO.rst b/TODO.rst
index fc87174..97aa56f 100644
--- a/TODO.rst
+++ b/TODO.rst
@@ -1,6 +1,6 @@
 DOCS 0.7.0
 ----------
-- ??? no sort in groupby
+- ???? no sort in groupby
 - DONE concat with dict
 - Gotchas re: integer indexing
```

These random outliers are making it hard to figure out what's really happening (the optimization I wanted to test seems to improve things by 25%-40% in a C testbed, but I can't get clean results.)

These tests aren't doing anything fancy either, so if they're affected, it's possible the entire suite is affected as well (just less dramatically...)

Possibly some combination of #3129, #3146 (cache and alignment) are related, or maybe some other source of non-determinism in Python and numpy. I can't reproduce this instability in C by trying to proxy it either by randomly adjusting byte alignment, but I haven't tried screwing around with memory paging yet.
