headers: normalize the spelling of some header guards

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/vcs-svn/line_buffer.h b/vcs-svn/line_buffer.h
index ee23b4f..e192aed 100644
--- a/vcs-svn/line_buffer.h
+++ b/vcs-svn/line_buffer.h
@@ -1,5 +1,5 @@
-#ifndef LINE_BUFFER_H_
-#define LINE_BUFFER_H_
+#ifndef LINE_BUFFER_H
+#define LINE_BUFFER_H
 
 #include "strbuf.h"