Cmd+b conflicts with the default keybinding for "build"

Cmd+B ("super+b") conflicts with the default keybinding for "build". See the file Packages/Default/Default (OSX).sublime-keymap:

```
{ "keys": ["super+b"], "command": "build" },
```

The recent change breaks the default keybinding. It took me a while to track the culprit to R Tools. Maybe it would be possible to setup a build system for R so that "build" command either launches R in batch mode, or sources the current file in the R GUI?