Various bug fixes

[Falcury]

Sorry about the so many separate things... I bundled some more bug fixes together, to avoid making pull requests for each separate issue. I hope that's OK.

• Fix error due to missing mkdir() argument on Linux
  • This fix was suggested by @EndeavourAccuracy
• Fix quickload penalty being applied even after time has stopped (obviously this should not happen...)
• Fix guard turning around immediately after quickloading
  • To reproduce the bug: in a room where a guard has not yet noticed you and has his back turned towards you, quicksave. Then alert the guard, so that he takes the active stance facing you. Then, still in the same room, quickload; then, the guard will immediately be facing you even though you have not alerted him.
• Silence warning about image 255 e.g. after entering an exit door
  • This happens after entering an exit door, because then the kid's frame is set to zero, and frame_table_kid[0].image == 255 (and image 255 does not exist).
• Fix feather fall effect being interrupted by the level door opening
  • This bug is noticable in original Level 7, if you trigger the level door while the weightless effect is still active.

[NagyD]

Fix feather fall effect being interrupted by the level door opening

Clarification: The feather fall music stops when the exit door finishes opening. This bug is present in the original game as well.

[NagyD]

Fix error due to missing mkdir() argument on Linux

I already did that here: 4a75006a9d65e6a86ddae519eadbb5d700403b0c

[Falcury]

I already did that here: 4a75006

Yes, you're right. Maybe I should not bundle separate stuff together like this, so it does not become a problem if one of the commits needs to be taken out.