Inconsistent behavior in modal window

[tmesser]

The "X" button on step 2 goes back one step instead of closing the little checkout modal.

[ihameed]

It's fine for the button to go back one step, because it's possible for there to be validation errors in step 1 that are only caught when trying to complete step 2, but it'd be nice if the user had some obvious way to go back to step 1 to correct the error; possibilities include having the validation failure direct the user to the first invalid field, having the little "X" button look like a back arrow, or making the flow headers ("1. Payment Info | 2. Shipping Info | etc.") clickable links that move between completed (or partially-completed) steps.