Fix directory creation to match actual OSX sematics as determined by adding

a few testcases ...
The basic method should fail if the directory already exists.
The intermediate directories method should fail if the directory exists unless
the option to create intermediate directories is selected, in which case a
pre-existing directory is counted as a success.

Tests/base/NSDistributedLock/basic.m

@@ -26,6 +26,7 @@ int main()
 
   [lock1 unlock];
   PASS(YES == [lock2 tryLock], "unlocking first lock allows second lock");
+  [lock2 unlock];
 
   END_SET("basic")
   return 0;