[FIX] trackers: Interpret checkbox values when importing in the same way as they are exported (i.e. y/n - thanks Geoff, hopefully fixes wish5467)

git-svn-id: file:///var/local/code.tiki.org/tikisvn/branches/13.x@52554 b456876b-0849-0410-b77d-98878d47e9d5