Make setCredentialsProvider more convenient to use

Change-Id: I984836ea7d6a67fd2d1d05f270afa7c29f30971c
Signed-off-by: Mathias Kinzler <mathias.kinzler@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/FetchCommand.java

 	/**
 	 * @param credentialsProvider
 	 *            the {@link CredentialsProvider} to use
+	 * @return {@code this}
 	 */
-	public void setCredentialsProvider(CredentialsProvider credentialsProvider) {
+	public FetchCommand setCredentialsProvider(
+			CredentialsProvider credentialsProvider) {
+		checkCallable();
 		this.credentialsProvider = credentialsProvider;
+		return this;
 	}
 }

org.eclipse.jgit/src/org/eclipse/jgit/api/PushCommand.java

 	/**
 	 * @param credentialsProvider
 	 *            the {@link CredentialsProvider} to use
+	 * @return {@code this}
 	 */
-	public void setCredentialsProvider(CredentialsProvider credentialsProvider) {
+	public PushCommand setCredentialsProvider(
+			CredentialsProvider credentialsProvider) {
+		checkCallable();
 		this.credentialsProvider = credentialsProvider;
+		return this;
 	}
 }