patchutils.py: Add tests for multiple patches in a single file.

staging/tests/multi.patch

@@ -0,0 +1,73 @@
+From be07df750862699f2515c0ac0ceb7a6c25e9458a Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?Author=20Name?= <author@email.com>
+Subject: [PATCH v3] component: Replace arg1 with arg2.
+
+Signed-off-by: =?UTF-8?q?Author=20Name?= <author@email.com>
+Signed-off-by: Other Developer <other@email.com>
+---
+ other_test.txt | 2 +-
+ test.txt       | 4 ++--
+ 2 files changed, 3 insertions(+), 3 deletions(-)
+
+diff --git a/other_test.txt b/other_test.txt
+index a26e3f5..187ea7d 100644
+--- a/other_test.txt
++++ b/other_test.txt
+@@ -1,7 +1,7 @@
+ other_line1();
+ other_line2();
+ other_line3();
+-function(arg1);
++function(arg2);
+ other_line4();
+ other_line5();
+ other_line6();
+diff --git a/test.txt b/test.txt
+index c9947e7..5d7eff8 100644
+--- a/test.txt
++++ b/test.txt
+@@ -1,7 +1,7 @@
+ line1();
+ line2();
+ line3();
+-function(arg1);
++function(arg2);
+ line5();
+ line6();
+ line7();
+@@ -9,7 +9,7 @@ line8();
+ line9();
+ line10();
+ line11();
+-function(arg1);
++function(arg2);
+ line12();
+ line13();
+ line14();
+-- 
+2.7.1
+
+From 801d4e778daf4f66dbe373e0a62cf0eb2fc0a7a3 Mon Sep 17 00:00:00 2001
+From: Other Developer <other@email.com>
+Subject: component: Replace arg2 with arg3. (v4)
+
+Signed-off-by: Other Developer <other@email.com>
+---
+ test.txt | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/test.txt b/test.txt
+index 5d7eff8..73811d5 100644
+--- a/test.txt
++++ b/test.txt
+@@ -1,7 +1,7 @@
+ line1();
+ line2();
+ line3();
+-function(arg2);
++function(arg3);
+ line5();
+ line6();
+ line7();
+-- 
+2.7.1