Add str.lower() for channel name to set_mask() and show_mask()

topic() calls lower() on the channel name, but not on set_mask() and show_mask(). If the channel name is not lower case, topic doesn't find the topic mask row in the database as the where condition is case sensitive. According to RFC2812 http://tools.ietf.org/html/rfc2812#section-1.3 channel names should be case insensitive, so lower() on all the channel names seems more appropriate than removing lower() from topic()
Add str.lower() to elif in during lookup in show_mask()

This needs to be lower()'d as well
Merge pull request #302 from Preston4tw/master

[adminchannel] Change .tmask and .showmask to treat channel name as case insensitive.
Merge pull request #301 from saltire/rss

Overhaul of RSS module
[rss] Download only feeds that have changed.

Downloading a feed for no reason, over and over again is really bad behavior.

- Adds a new column etag to the rss_feeds table.
[rss] Add publication time to the rss_feeds table.

Adding this before the actual code that needs it, because we are migrating
to new table anyway. This can be used later to detect when an entry has been
removed or modified.
[rss] Set default poll interval to a sane value.

Polling for rss feeds every 20 seconds is overkill. If fast response times
are needed, methods other than polling should be used.