Allow br tags as wrappers

The regex that invisimail uses currently only locates email addresses that are wrapped by p, li, or whitespace. TinyMCE and others can frequently wrap an email address in br tags. The pattern should be modified to allow <br /> as wrapping text as well.

I'm at work right now so can't roll a real patch, but I'm assigning this to myself as a reminder to do so when I get home. :-)