Move user eval function to be located on Lua registry.

Today, Redis wrap the user Lua code with a Lua function.
For example, assuming the user code is:

```
return redis.call('ping')
```

The actual code that would have sent to the Lua interpreter was:

```
f_b3a02c833904802db9c34a3cf1292eee3246df3c() return redis.call('ping') end
```

The wraped code would have been saved on the global dictionary with the
following name: `f_<script sha>` (in our example `f_b3a02c833904802db9c34a3cf1292eee3246df3c`).

This approach allows one user to easily override the implementation a another user code, example:

```
f_b3a02c833904802db9c34a3cf1292eee3246df3c = function() return 'hacked' end
```

Running the above code will cause `evalsha b3a02c833904802db9c34a3cf1292eee3246df3c 0` to return
hacked although it should have returned `pong`.

Another disadventage is that Redis basically runs code on the loading (compiling) phase without been
aware of it. User can do code injection like this:

```
return 1 end <run code on compling phase> function() return 1
```

The wraped code will look like this and the entire `<run code on compling phase>` block will run outside
of eval or evalsha context:

```
f_<sha>() return 1 end <run code on compling phase> function() return 1 end
```

0 files changed, 0 insertions, 0 deletions