Made writes to output window thread-safe

Reported by Jacob Nevins <jtn>

See bug #21896


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24892 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Added Achievement type "Lucky"

See patch #4692


git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24894 a0f10bec-cc02-0410-94fc-a9cfff90b4cd
Don't overwrite the link text when the links have been generated by the server.

From a report by log65536

See gna bug #21326

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24895 a0f10bec-cc02-0410-94fc-a9cfff90b4cd