Redis EVAL and EVALSHA fixes and tests.

Fixed:

* EVAL and EVALSHA need numKeys as first argument after script / SHA otherwise ERR is thrown - http://redis.io/commands/EVAL
* When calling an aliased method with `__call()` only `$args` should be passed as arguments.

Added:

* Tests for `eval()`, `evalSha()` and `script()`
* Aliases for `eval` and `evaluate` to `_eval`, `evalSha` and `evaluateSha` to `_evalSha`
* Function `doProcessVariantResponse()` to process multibulk responses.