Fix directory creation to use low level methods which consider the presence

of an existing directory to be an error, rather than the NSFileManager methods
that consider it a success.  The logic of distributed locking requires us to
fail if a directory already exists.

Tests/base/NSDistributedLock/basic.m

@@ -0,0 +1,32 @@
+#import "ObjectTesting.h"
+#import <Foundation/NSDistributedLock.h>
+#import <Foundation/NSFileManager.h>
+
+int main()
+{
+  START_SET("basic")
+
+  NSString              *path;
+  NSDistributedLock     *lock1;
+  NSDistributedLock     *lock2;
+  
+  test_NSObject(@"NSDistributedLock",
+    [NSArray arrayWithObject: [NSDistributedLock new]]);
+
+  path = [[NSFileManager defaultManager] currentDirectoryPath];
+  path = [path stringByAppendingPathComponent: @"MyLock"];
+  lock1 = [NSDistributedLock lockWithPath: path];
+  lock2 = [NSDistributedLock lockWithPath: path];
+
+  PASS(lock1 != lock2, "locks with the same path differ");
+
+  PASS(YES == [lock1 tryLock], "we can lock the first lock");
+
+  PASS(NO == [lock2 tryLock], "the locks are exclusive");
+
+  [lock1 unlock];
+  PASS(YES == [lock2 tryLock], "unlocking first lock allows second lock");
+
+  END_SET("basic")
+  return 0;
+}