Internalized feed favicon fetching.

Locate and cache favicons from feed sites without relying on an external service.
This is still a bit rough around the edges, but seems to be functional.
Fixes to FavIcon handling.  Image cache now behaves more like cache.

A feed update will re-fetch the feed image if the current image cache file does not exist on disk.

Quelled 'undefined offset' notices arising from using list()=explode() to parse strings.
Check more variables for null values before trying to use them.
Simplified link-element processing.
FavIcon absolute urls are now constructed correctly.

Removed redundant fetch when storing favicon data into cache.
Removed third-party favicon handling.

The new favicon class seems to be working well enough, so the vestiges of the old external fvicon.com service have been excised.
FavIcon now requests plainly encoded responses from urls.

PHP's http-stream dingus doesn't seem able to automatically handle compressed content-encodings, so as a quick fix FavIcon now requests that all responses be uncompressed.
Less plugin spam in logs.  Removed useless define from config.

Included plugins are now listed on one line, rather than one per.

Removed unused (and redundant) 'DIR_SEP' define from sample config.
Fix OPML import for URLs with entities in them (although there is a deeper problem)
install.php migrations are now optimistic.

All table updates will now be attempted, rather than giving up at the first sign of failure.
Merge pull request #2 from plaidfluff/master

Fix OPML import for URLs with entities in them (although there is a deep...
Changed OPML parser to use an actual XML parser
Merge pull request #3 from plaidfluff/master

Changed OPML parser to use an actual XML parser