mailinfo: feed only one line to handle_filter() for QP input

The function is intended to be fed one logical line at a time to
inspect, but a QP encoded raw input line can have more than one
lines, just like BASE64 encoded one.

Quoting LF as =0A may be unusual but RFC2045 allows it.

The issue was noticed and fixed by Jay Soffian.  JC added a test
to protect the fix from regressing later.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-mailinfo.c

@@ -818,6 +818,7 @@ static void handle_body(void)
 
 		switch (transfer_encoding) {
 		case TE_BASE64:
+		case TE_QP:
 		{
 			char *op = line;
 

t/t5100-mailinfo.sh

@@ -11,7 +11,7 @@ test_expect_success 'split sample box' \
 	'git mailsplit -o. ../t5100/sample.mbox >last &&
 	last=`cat last` &&
 	echo total is $last &&
-	test `cat last` = 8'
+	test `cat last` = 9'
 
 for mail in `echo 00*`
 do

t/t5100/info0009

@@ -0,0 +1,5 @@
+Author: F U Bar
+Email: f.u.bar@example.com
+Subject: updates
+Date: Mon, 17 Sep 2001 00:00:00 +0900
+

t/t5100/msg0009

@@ -0,0 +1,2 @@
+This is to fix diff-format documentation.
+

t/t5100/patch0009

@@ -0,0 +1,13 @@
+diff --git a/Documentation/diff-format.txt b/Documentation/diff-format.txt
+index b426a14..97756ec 100644
+--- a/Documentation/diff-format.txt
++++ b/Documentation/diff-format.txt
+@@ -81,7 +81,7 @@ The "diff" formatting options can be customized via the
+ environment variable 'GIT_DIFF_OPTS'.  For example, if you
+ prefer context diff:
+ 
+-      GIT_DIFF_OPTS=-c git-diff-index -p $(cat .git/HEAD)
++      GIT_DIFF_OPTS=-c git-diff-index -p HEAD
+ 
+ 
+ 2. When the environment variable 'GIT_EXTERNAL_DIFF' is set, the

t/t5100/sample.mbox

@@ -407,3 +407,26 @@ Subject: [PATCH] another patch
 
 Hey you forgot the patch!
 
+From nobody Mon Sep 17 00:00:00 2001
+From: A U Thor <a.u.thor@example.com>
+Date: Mon, 17 Sep 2001 00:00:00 +0900
+Mime-Version: 1.0
+Content-Type: Text/Plain; charset=us-ascii
+Content-Transfer-Encoding: Quoted-Printable
+
+=0A=0AFrom: F U Bar <f.u.bar@example.com>
+Subject: [PATCH] updates=0A=0AThis is to fix diff-format documentation.
+
+diff --git a/Documentation/diff-format.txt b/Documentation/diff-format.txt
+index b426a14..97756ec 100644
+--- a/Documentation/diff-format.txt
++++ b/Documentation/diff-format.txt
+@@ -81,7 +81,7 @@ The "diff" formatting options can be customized via the
+ environment variable 'GIT_DIFF_OPTS'.  For example, if you
+ prefer context diff:
+=20
+-      GIT_DIFF_OPTS=3D-c git-diff-index -p $(cat .git/HEAD)
++      GIT_DIFF_OPTS=3D-c git-diff-index -p HEAD
+=20
+=20
+ 2. When the environment variable 'GIT_EXTERNAL_DIFF' is set, the