Summary:
tweakdefaults renamed core hg's `grep` to `histgrep`, and added a `hg grep` that behaves more like `git grep`, searching the working copy. This diff folds those changes into core.
The config changes from
```
[tweakdefaults]
allowfullrepohistgrep = False
```
to
```
[histgrep]
allowfullrepogrep = False
```
Reviewed By: quark-zju
Differential Revision: D10435279
fbshipit-source-id: ad3d1da5824511a612111715e46119d70066050f
