diff: correct newline in summary for renamed files

In 146fdb0dfe (diff.c: emit_diff_symbol learns about DIFF_SYMBOL_SUMMARY,
2017-06-29), the conversion from direct printing to the symbol emission
dropped the new line character for renamed, copied and rewritten files.

Add the emission of a newline, add a test for this case.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Stefan Beller <sbeller@google.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4013/diff.diff-tree_--stat_initial_mode

@@ -0,0 +1,4 @@
+$ git diff-tree --stat initial mode
+ file0 | 0
+ 1 file changed, 0 insertions(+), 0 deletions(-)
+$

t/t4013/diff.diff-tree_--summary_initial_mode

@@ -0,0 +1,3 @@
+$ git diff-tree --summary initial mode
+ mode change 100644 => 100755 file0
+$

t/t4013/diff.diff-tree_initial_mode

@@ -0,0 +1,3 @@
+$ git diff-tree initial mode
+:100644 100755 01e79c32a8c99c557f0757da7cb6d65b3414466d 01e79c32a8c99c557f0757da7cb6d65b3414466d M	file0
+$

t/t4013/diff.log_--decorate=full_--all

@@ -1,4 +1,10 @@
 $ git log --decorate=full --all
+commit b7e0bc69303b488b47deca799a7d723971dfa6cd (refs/heads/mode)
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:06:00 2006 +0000
+
+    update mode
+
 commit cd4e72fd96faed3f0ba949dc42967430374e2290 (refs/heads/rearrange)
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:06:00 2006 +0000

t/t4013/diff.log_--decorate_--all

@@ -1,4 +1,10 @@
 $ git log --decorate --all
+commit b7e0bc69303b488b47deca799a7d723971dfa6cd (mode)
+Author: A U Thor <author@example.com>
+Date:   Mon Jun 26 00:06:00 2006 +0000
+
+    update mode
+
 commit cd4e72fd96faed3f0ba949dc42967430374e2290 (rearrange)
 Author: A U Thor <author@example.com>
 Date:   Mon Jun 26 00:06:00 2006 +0000