#3 executeable lock is not released occationally

[Georg Martius]

Sometimes the lock on the executable is not deleted and then hinders the transfer of a newer executable. This is very painful since the client does not complain about it and uses the old executable.

Solutions:
- use proper filesystem locks
- make the lock session specific
- client should complain and die
- copy entire session into another folder, so that different sessions do not clash (anyway a good idea) However then reuse of the file is not possible over several sessions