Added 'application/x-download' to the set of types that can be imported

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2880 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Fixed bug which caused the day and week views to be displayed incorrectly if the brief description was blank ('') - which of course shouldn't normally happen.  (See thread on mailing list with subject "Day/week tables displaying incorrectly")

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2881 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7