Nightly build failed

[Geert Janssens]

The windows build failed this night.

I have traced it back to the modifications to assert_one_dir I committed 
yesterday. There seems to be an odd bug in Msys that the function crashes the 
shell in this construct:
{
  [[ <some test> ]] && die <some message>
}

The critical part appears to be that there is no normal command between this 
statement and the closing parenthesis. Changing this to:
{
  [[ <some test> ]] && die <some message>
  echo -n
}
no longer crashes.
Also this bug is not triggered in an interactive shell. That's why I didn't 
experience this before I committed.

I don't feel like getting to the bottom of this, so I simply rewrote the 
function to avoid this bug.

The next nightly build should be fine again.

Geert