[REL] Preparing release

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/6.x@48214 b456876b-0849-0410-b77d-98878d47e9d5
[REL] Update README file for 6.13

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/6.x@48215 b456876b-0849-0410-b77d-98878d47e9d5
[REL] Update changelog.txt for 6.13

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/6.x@48216 b456876b-0849-0410-b77d-98878d47e9d5
[REL] Update copyright.txt for 6.13

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/6.x@48217 b456876b-0849-0410-b77d-98878d47e9d5