Support extension of TransportHttp

This allows subclasses to configure the HTTP connection (for example,
to add headers to the request).

Bug: 400724
Change-Id: I6f9d699e158a7b9d813c8fa8d273992a28994e41
Signed-off-by: Michael Nelson <michael.nelson@tasktop.com>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/transport/TransportHttp.java

@@ -504,7 +504,16 @@ public class TransportHttp extends HttpTransport implements WalkTransport,
 		return httpOpen(METHOD_GET, u);
 	}
 
-	final HttpURLConnection httpOpen(String method, URL u) throws IOException {
+	/**
+	 * Open an HTTP connection.
+	 *
+	 * @param method
+	 * @param u
+	 * @return the connection
+	 * @throws IOException
+	 */
+	protected HttpURLConnection httpOpen(String method, URL u)
+			throws IOException {
 		final Proxy proxy = HttpSupport.proxyFor(proxySelector, u);
 		HttpURLConnection conn = (HttpURLConnection) u.openConnection(proxy);