Make --git-dir optional for 'jgit init'

For compatibility reasons with regards to native git and also to
make the init command easier to use from the command line,
argument --git-dir should not be required.

Additionally the path created in case --git-dir is not supplied now is
canonical and thus easier to read.

Change-Id: Idb7d77e983a78c4b21fbf232fc1e75ef581e5ed1
Signed-off-by: Philipp Thun <philipp.thun@sap.com>

org.eclipse.jgit.pgm/src/org/eclipse/jgit/pgm/Init.java

@@ -69,7 +69,8 @@ class Init extends TextBuiltin {
 	protected void run() throws Exception {
 		InitCommand command = Git.init();
 		command.setBare(bare);
-		command.setDirectory(new File(gitdir));
+		if (gitdir != null)
+			command.setDirectory(new File(gitdir));
 		Repository repository = command.call().getRepository();
 		out.println(MessageFormat.format(
 				CLIText.get().initializedEmptyGitRepositoryIn, repository

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

@@ -83,7 +83,7 @@ public class InitCommand implements Callable<Git> {
 			} else if (builder.getGitDir() == null) {
 				File d = new File(".");
 				if (!bare)
-					d = new File(d, Constants.DOT_GIT);
+					d = new File(d, Constants.DOT_GIT).getCanonicalFile();
 				builder.setGitDir(d);
 			}
 			Repository repository = builder.build();