gnu: tidy: Add fixes for CVE-2015-5522 and CVE-2015-5523.

* gnu/packages/patches/tidy-CVE-2015-5522+5523.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/web.scm (tidy)[source]: Add patch.

gnu-system.am

@@ -619,6 +619,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/teckit-cstdio.patch			\
   gnu/packages/patches/texi2html-document-encoding.patch	\
   gnu/packages/patches/texi2html-i18n.patch			\
+  gnu/packages/patches/tidy-CVE-2015-5522+5523.patch		\
   gnu/packages/patches/tvtime-gcc41.patch			\
   gnu/packages/patches/tvtime-pngoutput.patch			\
   gnu/packages/patches/tvtime-videodev2.patch			\

gnu/packages/patches/tidy-CVE-2015-5522+5523.patch

@@ -0,0 +1,36 @@
+Copied from Debian.
+
+From c18f27a58792f7fbd0b30a0ff50d6b40a82f940d Mon Sep 17 00:00:00 2001
+From: Geoff McLane <ubuntu@geoffair.info>
+Date: Wed, 3 Jun 2015 20:26:03 +0200
+Subject: [PATCH] Issue #217 - avoid len going negative, ever...
+
+---
+ src/lexer.c | 8 +++++---
+ 1 file changed, 5 insertions(+), 3 deletions(-)
+
+diff --git a/src/lexer.c b/src/lexer.c
+index 376a3d8..664f806 100644
+--- a/src/lexer.c
++++ b/src/lexer.c
+@@ -3739,16 +3740,17 @@ static tmbstr ParseValue( TidyDocImpl* doc, ctmbstr name,
+         /* and prompts attributes unless --literal-attributes is set to yes      */
+         /* #994841 - Whitespace is removed from value attributes                 */
+ 
+-        if (munge &&
++        /* Issue #217 - Also only if/while (len > 0) - MUST NEVER GO NEGATIVE! */
++        if ((len > 0) && munge &&
+             TY_(tmbstrcasecmp)(name, "alt") &&
+             TY_(tmbstrcasecmp)(name, "title") &&
+             TY_(tmbstrcasecmp)(name, "value") &&
+             TY_(tmbstrcasecmp)(name, "prompt"))
+         {
+-            while (TY_(IsWhite)(lexer->lexbuf[start+len-1]))
++            while (TY_(IsWhite)(lexer->lexbuf[start+len-1]) && (len > 0))
+                 --len;
+ 
+-            while (TY_(IsWhite)(lexer->lexbuf[start]) && start < len)
++            while (TY_(IsWhite)(lexer->lexbuf[start]) && (start < len) && (len > 0))
+             {
+                 ++start;
+                 --len;

gnu/packages/web.scm

@@ -381,7 +381,8 @@ (module "tidy")
                     (revision "2009-12-23")))
               (sha256
                (base32
-                "14dsnmirjcrvwsffqp3as70qr6bbfaig2fv3zvs5g7005jrsbvpb"))))
+                "14dsnmirjcrvwsffqp3as70qr6bbfaig2fv3zvs5g7005jrsbvpb"))
+              (patches (list (search-patch "tidy-CVE-2015-5522+5523.patch")))))
     (build-system gnu-build-system)
     (arguments
      '(#:phases (alist-cons-after