Merge pull request #16 from elahurd/master

fixed duplicate function issue, now redirects to shopping cart on error
Merge pull request #17 from elahurd/master

tested against osCommerce 2.3.4
Merge pull request #18 from elahurd/master

updated header to reflect latest version, updated README
Merge pull request #1 from bitpay/master

Sync with BitPay repo
Added error msgs when core funcs not available

Also added default case in the event an unhandled IPN status is sent
Fixed invoice error handling & code cleanup

Fixed deprecated uses of the old PHP4-style var keyword
Merge pull request #19 from ionux/master

Fixed invoice error handling
fixed parameters for tep_href_link and tep_redirect