Fixed variable error in wpsc-shipping/usps_20.php

The variable being tested is NOT the one being assigned the new instance of ASHTools().
Filter gateway checkout form output
Add docblocks for all functions in gateways.php
Fix instances of "siteurl" that should use home_url().
Remove unused  $siteurl references.
Use site_url() instead of get_option( 'siteurl' ).
Use admin_url() instead of "siteurl" for admin URLs.
home_url() should include slash when adding query args. Props meloniq
Use get_edit_post_link() for product edit link. Props meloniq
Adding four new filters on purchase log SQL Query

Primary use case in my head here is for plugins using wpsc_sales_log_process_bulk_action and wpsc_sales_log_process_extra_tablenav - they should be able to easily filter the actual SQL query, not the items returned.
move payment gateway settings inline, removing the settings sidebar.
render list of payment gateways more similar to the wordpress plugins page.
improve handling of display names for payment gateways
add current display name to payment gateway table. improve cancel button on payment gateway settings rows.
improve layout of settings form and buttons in payment gateways table
improved rendering of marketing section of admin panel
Added filters to the rates in the usps shipping

Added two filters for both International and Domestic shipping rates so plugins can hook them and apply any additional fees, etc. without altering the WP-e-Commerce core code.
Added shipwire option to installer

The shipwire option cannot be saved in the *Shipping* settings since a default value/option wasn't being created upon install of WP-e-Commerce.
Merge pull request #345 from amereservant/patch-4

Added shipwire option to installer
Filtering $total_where variable