Be careful in createTemporaryDirectory() when removing existing files

If File.exists() returns true, it might be a regular file being in
the way, after all...

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

src/main/java/org/scijava/test/TestUtils.java

@@ -119,7 +119,10 @@ public static File createTemporaryDirectory(final String prefix,
 		}
 
 		final File file = new File(baseDirectory, prefix + suffix);
-		if (file.exists()) FileUtils.deleteRecursively(file);
+		if (file.isDirectory()) FileUtils.deleteRecursively(file);
+		else if (file.exists() && !file.delete()) {
+			throw new IOException("Could not remove " + file);
+		}
 		if (!file.mkdir()) throw new IOException("Could not make directory " + file);
 		return file;
 	}