A few fixes to the WordPress importer

[briancolinger]

Cast $_POSTauthor_in as array to fix a PHP warning.

Adding status messages about categories, tags, and terms.

Adding zero length filesize check.

Adding bump_request_timeout to http_request_timeout hook.
This will give the importer more time for fetching attachments.

Adding post guid to url_remap

[ryan]

(In [13735]) WP importer fixes. Props briancolinger. fixes #12619