Merge branch 'master' into jgrpp

# Conflicts:
#	src/fontcache.cpp
#	src/openttd.cpp
#	src/os/macosx/font_osx.cpp
#	src/os/unix/font_unix.cpp
#	src/os/windows/font_win32.cpp
#	src/strings.cpp

src/object_cmd.cpp

@@ -401,6 +401,8 @@ CommandCost CmdBuildObject(TileIndex tile, DoCommandFlag flags, uint32 p1, uint3
 		case OBJECT_HQ: {
 			Company *c = Company::Get(_current_company);
 			if (c->location_of_HQ != INVALID_TILE) {
+				/* Don't relocate HQ on the same location. */
+				if (c->location_of_HQ == tile) return_cmd_error(STR_ERROR_ALREADY_BUILT);
 				/* We need to persuade a bit harder to remove the old HQ. */
 				_current_company = OWNER_WATER;
 				cost.AddCost(ClearTile_Object(c->location_of_HQ, flags));