-E option now represents html url extension

This is useful for URL rewriting. The -E option was previously used to denote an
empty -e and can still be done with `-e ''`. To use a URL rewriting scheme that
removes the extension, use -E ''.

To support this change properly, and to support users who may not want to use
`.' as their extension prefix, it is no longer automatically added.

(This breaks backwards compatibility, but -E was pushed publically so recently
that this change is likely to affect anyone but, well, me.)
Added -P to msgfmt for rss subject line generation

Whoops; <p> tags were being included in RSS titles.