Xconq GDL change

[Hans Ronne]

The bigicons gvar is no longer supported. If you used it in a game file,
just remove it. Xconq now automatically detects if you are using big
Civ-type icons and adjusts drawing accordingly.

Other changes:

A serious bug that caused some units to hang with an obsolete build task
has been fixed.

Drawing of emblems and multiple units has been fixed so that images always
stay within a cell (no garbage left on the map after a move).

Various other bug fixes. See the ChangeLog.

Hans