Custom Spray in L4D2

A common problem problem in Left 4 Dead 2 in Steam on Linux seems to be when attempting to import sprays, resulting in the error:

Spray Import Error
Unable to write output spray file. It's possible the current user doesn't have permission.

Whether this happens in other source games also, I do not know, however the fix should be the same.

L4D2 seems to perform half of the action needed, it just has problems when copying the actual image file into the folder it needs to be in.

So here is the remedy: