Update buffer-mgr concurrency test to close files

The Buffer Manager concurrency test wasn't closing the data files it
created, so they couldn't be deleted during the cleanup phase on
Windows.  This caused test failures on Windows but not on *nix.

src/test/java/edu/caltech/test/nanodb/storage/TestBufferManager.java

@@ -57,6 +57,9 @@ public class TestBufferManager extends StorageTestCase {
 
         verify(fileMgr, times(1)).loadPage(file, 3, page3.getPageData(), true);
         verify(fileMgr, times(1)).loadPage(file, 5, page.getPageData(), true);
+
+        bufMgr.removeDBFile(file);
+        fileMgr.closeDBFile(file);
     }
 
 
@@ -93,7 +96,7 @@ public class TestBufferManager extends StorageTestCase {
         }
 
         // Give the test 60 seconds to complete.
-        Concurrent.assertConcurrent("Concurrent reads and writes", tasks, 60);
+        Concurrent.assertConcurrent("Concurrent reads and writes", tasks, 120);
     }
 
 
@@ -143,5 +146,9 @@ public class TestBufferManager extends StorageTestCase {
 
             page.unpin();
         }
+
+        // Close the data file.
+        bufMgr.removeDBFile(file);
+        fileMgr.closeDBFile(file);
     }
 }