Simplify regexp that escapes regexp special characters.
Add deep comparison note to the `_.where` docs. [ci skip]
Simplify regexp that escapes special regexp characters for `reNative`, and add `callback` and `thisArg` arguments to `_.clone`, `_.cloneDeep`, and `_.isEqual`.
Add `underscore` build replacement for `_.isEqual` and ensure `legacy` cannot be used with `backbone` or `underscore` commands.
Cleanup unit tests and tests for `_.clone`, `_.cloneDeep`, and `_.isEqual` support of `callback` and `thisArg` arguments.