Allow commandline tests to use raw output

Allow commandline tests to use raw output

Introduce a new CLIGitCommand.rawExecute() helper that behaves
just like execute() except that instead of processing its output
it returns it raw.

So now you can do

	final byte[] expect = { 0, 1, 2, 3 };
	final byte[] actual = CLIGitCommand.rawExecute(
			"git show HEAD:goo.raw", db);
	assertArrayEquals(expect, actual);

to test the output from "git show HEAD:goo.raw" without being
distracted by encoding issues.

Noticed while writing tests for a new "jgit archive" command that
writes its output in ZIP format.

Change-Id: I2fe6020a537975d0ccf414b7125d85d6cd86898c