script: create "script" directory on each action (just in case it has been removed) (bug #38472)
scripts: create directories (language and language/autoload) on each action (install/remove/autoload), just in case they have been removed (bug #38473)
core: fix refresh of item "completion" (bug #38214) (patch from Nils Görs)

The item is now cleared after any action that is changing content of command
line and after switch of buffer.