Bumping the revision number to 0.24.  Yeah!

git-svn-id: svn://dev.exiv2.org/svn@3088 b7c8b350-86e7-0310-a4b4-de8f6a8f16a3
Bumping the copyright notice in src &samples from 2012 to 2013

git-svn-id: svn://dev.exiv2.org/svn@3089 b7c8b350-86e7-0310-a4b4-de8f6a8f16a3