Upgraded Mail_Mime package to Version 1.8.8

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2829 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7
Added a LAST-MODIFIED property to all VEVENTS

git-svn-id: http://svn.code.sf.net/p/mrbs/code/mrbs/trunk@2830 25f7e783-145e-4f2d-a9f8-dd7182bfe9c7