Fixed bug #21486: Team label clears a non-team label

Editing a non-team label to be a team label no longer removes the old label (ie, everyone not in that team can still see it).

https://gna.org/bugs/index.php?21486

Signed-off-by: hp <sachith500@ubuntu.(none)>
Signed-off-by: Sachith Hasaranga Seneviratne <sachith500@gmail.com>

Added changelog entries and updated about.cfg
Added changelog entries and updated about.cfg. Minor typo-fix in
changelog.

Signed-off-by: Sachith Hasaranga Seneviratne <sachith500@gmail.com>
Merge branch 'bug21486' of github.com:sachith500/wesnoth-old (PR #94)