diff, log -p: do not use outs before it is initialized

diff, log -p: do not use outs before it is initialized

Since commit caa362f20df1 (Check for write errors in standard out and
exit with error, 2012-09-14), running "jgit diff" results in a
NullPointerException:

| $ jgit diff
| java.lang.NullPointerException
|	at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
|	at java.io.BufferedOutputStream.write(BufferedOutputStream.java:126)
|	at org.eclipse.jgit.diff.DiffFormatter.format(DiffFormatter.java:688)
|	at org.eclipse.jgit.diff.DiffFormatter.format(DiffFormatter.java:630)
|	at org.eclipse.jgit.diff.DiffFormatter.format(DiffFormatter.java:616)
|	at org.eclipse.jgit.diff.DiffFormatter.format(DiffFormatter.java:600)
|	at org.eclipse.jgit.pgm.Diff.run(Diff.java:211)
|	at org.eclipse.jgit.pgm.TextBuiltin.execute(TextBuiltin.java:166)
|	at org.eclipse.jgit.pgm.Main.execute(Main.java:200)
|	at org.eclipse.jgit.pgm.Main.run(Main.java:120)
|	at org.eclipse.jgit.pgm.Main.main(Main.java:94)

That patch replaced most uses of System.out with a wrapper, with
changes like the following:

	 class Diff extends TextBuiltin {
		private final DiffFormatter diffFmt = new DiffFormatter( //
	-			new BufferedOutputStream(System.out));
	+			new BufferedOutputStream(outs));

outs is not set for TextBuiltin objects until init() has been run.
Moving the initialization to after the super.init() call gets
"jgit diff" and "jgit log -p" working well again.

Change-Id: I80fcf259c4fb733990bd16e52bcf94e66d820826