Fixes:
- Selected TDM FM was not updated on refresh from disk.
- Selected TDM FM was not updated if the FM was deselected in-game.
- An optimization was broken which caused a refresh from disk even when unnecessary.
- We no longer pass the FM as an argument to the game, but rather simply write it out to currentfm.txt. This avoids an issue where if you pass an FM as an argument to the game (+set fs_currentfm some_fm), then you deselect the FM or select another one, upon game restart it will re-select the FM you initially passed, thus effectively preventing any change of selection unless you quit and start again manually.