Add exact line test for TextFragment#ApplyStrict

This ensures the line number is used and application isn't based only on
matching context lines.

Author: bluekeyes

gitdiff/apply_test.go

@@ -23,6 +23,7 @@ func TestTextFragmentApplyStrict(t *testing.T) {
 		"changeStart":       {File: "change_start"},
 		"changeMiddle":      {File: "change_middle"},
 		"changeEnd":         {File: "change_end"},
+		"changeExact":       {File: "change_exact"},
 		"changeSingleNoEOL": {File: "change_single_noeol"},
 	}
 

gitdiff/testdata/apply/text_fragment_change_exact.dst

@@ -0,0 +1,19 @@
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+new line a
+line
+line
+line

gitdiff/testdata/apply/text_fragment_change_exact.patch

@@ -0,0 +1,12 @@
+diff --git a/gitdiff/testdata/apply/text_fragment_change_exact.src b/gitdiff/testdata/apply/text_fragment_change_exact.src
+--- a/gitdiff/testdata/apply/text_fragment_change_exact.src
++++ b/gitdiff/testdata/apply/text_fragment_change_exact.src
+@@ -13,7 +13,7 @@ line
+ line
+ line
+ line
+-line
++new line a
+ line
+ line
+ line

gitdiff/testdata/apply/text_fragment_change_exact.src

@@ -0,0 +1,30 @@
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line
+line