multilingual capable bulk operations settings

I've found that this module doesn't work very well with the internationalization module. Every time you translate a string contented in any of the labels used by an operation it looses all the settings for all bulk operation views. This is because the key used for the array containing the data for each operation is its label. I enclose a patch that fixes this problem by using the callback function instead. I added some t() functions in other places so you don't need to add a specific i18n variable the labels translated to any language other than English.