Left over blogapi bugs (from new xmlrpc code migration)

This patch fixes a handful of things that were broken in the switch to chx's new xmlrpc code. Here's a quick recap:

* blogger.getPost was missing
* blogger.getUsersBlogs was missing its parameters
* metaweblog.newMediaObject wasn't returning the url properly
* typo in blogapi_metaweblog_get_recent_posts
* leftover scalarval() mt_set_post_categories
* reference to old iso8601_decode