2 bugfixes on the ufo2map tool

[rxadmin]

• fix: -gamedir entry is now converted to ufo-path style separaters

• before storing it in config.gamedir

• fix: if -gamedir is specified, the map specified is checked against

• the value of -gamedir and changed to a relative path before continuing;

• this was because the ufo-filesystem has problems with a full path

• specification of the map on the command line

[DarkRainX]

I've applied your changes to master, thank!