Merge branch...

Merge branch '78-errno-115-returned-on-successful-completion-for-several-system-calls' into 'master'

This fix contains three parts:

1. errno 115 was leaked during initialization of the client in
   init_ld_environment_(). However, the value on its own is irrelevant to
   this issue as all internal errno variable changes should be kept
   internal as it is the case during each syscall intercept hook.
   Therefore, the original errno variable is restored after the
   initialization finishes.
2. lseek() tests revealed that whence SEEK_SET was not handled
   correctly. It should not allow negative offsets.

3. All FIXME TODOs in the testing code have been removed including
   testing on the errno in a successful case because it is undefined.

Resolve "Errno 115 returned on successful completion for several system calls"

Closes #78

See merge request hpc/gekkofs!65