Sending pull request to sync my repo (minor version typo fix/es_ES po/mo files fix)

I've just started getting acquainted with GitHub, so I apologize for any confusions I may cause. 

This pull request includes the following:
1. Fix typo in wpsc_minor_option check in wpsc_install().
2. Certain Cart/Checkout translation terms are missing or exist but are not found in wpsc-es_ES.mo

I'm looking to sync these fixes with this pull request before I apply the shipping helper/UPS/USPS changes to avoid sending too many fixes at a time. The resulting MO file was tested to verify that the missing/not found translations are visible:
![wp-e-commerce3081219_1](https://f.cloud.github.com/assets/5473636/1788234/ff8c9808-6920-11e3-8512-2fe6b2eb55ca.jpg)
 
If you require any additional information, please don't hesitate to ask.

Jorge