Shipping method before/after actions.
Added actions to notify that shipping method processing is about to start, or has just compelted.
This actions are useful if you want to handle errors or conditions generated by shipping modules.
Performance addendum for filters PR
Shipping methods are calcualted whether or not all of the information is available for the calcualtion.
This can take a long time, expecially when shipping methods require some minimum set of information.  The
filter added allows a theme, plugin or or a shipping module to prevent the time consuming calulation and
perhaps even record record an error or present an informitive message.

When combined with the new customer profile infrastructre this can have a positive impact on performance and
cehckout flow.
added missing quotes to filter name
Merge pull request #851 from JeffPyeBrook/shipping-method-actions

Shipping method before/after actions.
Allow actual prices and weights with hundredths, rather than tenths.  What the heck man.
Merge branch 'master' of github.com:wp-e-commerce/WP-e-Commerce
The UI label was incorrect here - the box should be checked if you are NOT shipping thi sproduct.  Super confusing.
Edit Shipping link inside Variations metabox has one major flaw - it can set, but not unset, product meta.  Not usually a problem for weight and pricing fields, but huge problem for the no shipping metabox. Needs some rethinking here, but this should resolve the main issue of not being able to unset that box.
Add ability to define some cosntants in WP_CONFIG if desired
Detect cache enabled from WordPRess settings.
Allow cache config to be set in WP_CONFIG.PHP
Cart Widget will now respect cache detection setting.
Check using $cache_enabled setting removed becuase that setting can't be found in WordPress documentation.
WP_CACHE defined constant user per documentation here http://codex.wordpress.org/Editing_wp-config.php#Cache
meta key translation for future upgrade implementation begins
Fix typo in function call name
Fix return value in utility function to return custom keys
Fix incorrect variable name in get custom values utility function
more translation implementation
Error notices on latest master and UPS

`Notice: Undefined variable: wpec_ash_tools in D:\wamp\www\latestwpec\wp-content\plugins\WP-e-Commerce-master\wpsc-shipping\ups_20.php on line 752`

Adding the $wpec_ash_tools to the globals seems to fix it. I looked at USPS and usps has it in the globals so i based my change on that
Split load checkout data into two functions, wpsc_checkout_form_fields and wpsc_checkout_unique_names
New functions ruturn arrays of values
Pass each meta key through a validation function
Implemented visitor meta meta key alias function.
IMplemented visitor meta key database upgrade function.
completed visitor meta key alias function implementation
added check to prevent internal meta keys from being aliased