FREAD_READS_DIRECTORIES test fails for the wrong reasons

A while ago, the configure test for FREAD_READS_DIRECTORIES was changed to (attempt to) check for a NULL result from fopen. Unfortunately, the test will always fail - because it won't compile. The code snippet in configure.ac translates to:

return f);

Either there's an extra ) or a missing (. A cast to int wouldn't hurt either.

I'd supply a patch to fix this, but I'm not sure what the results of suddenly fixing the test would be. It seems to work well on my machine, but I don't stress git much here, and it's just one machine.