xfstests: add a unified diff option

Add the -udiff option to the test driver to make test output more
easily readable.

[hch:  made -udiff the default]

Reviewed-by: Christoph Hellwig <hch@lst.de>

common

@@ -19,7 +19,7 @@ _setenvironment
 
 check=${check-true}
 
-diff=diff
+diff="diff -u"
 verbose=false
 group=false
 xgroup=false
@@ -105,8 +105,9 @@ check options
     -xfs                test XFS (default)
     -udf                test UDF
     -nfs                test NFS
-    -l			line mode diff (default)
+    -l			line mode diff
     -xdiff		graphical mode diff
+    -udiff		show unified diff (default)
     -n			show me, do not run tests
     -q			quick [deprecated]
     -T			output timestamps
@@ -141,7 +142,8 @@ testlist options
 	    xpand=false
 	    ;;
 
-	-l)	# line mode for diff, default now, keep for backward compat
+	-l)	# line mode for diff, was default before
+	    diff="diff"
 	    xpand=false
 	    ;;
 
@@ -157,6 +159,11 @@ testlist options
 	    fi
 	    ;;
 
+	-udiff) # show a unified diff, default now, keep for backward compat
+	    xpand=false
+	    diff="$diff -u"
+	    ;;
+
 	-q)	# "quick", no longer used - always quick :-)
 	    xpand=false
 	    ;;