gnu: unzip: Reorganize security fixes for improved clarity.

* gnu/packages/patches/unzip-fix-overflows-and-infloop.patch: Delete
  file.  Its contents are now split into the following new files:
* gnu/packages/patches/unzip-CVE-2015-7696.patch,
  gnu/packages/patches/unzip-CVE-2015-7697.patch,
  gnu/packages/patches/unzip-overflow-on-invalid-input.patch: New files.
* gnu-system.am (dist_patch_DATA): Adjust accordingly.
* gnu/packages/zip.scm (unzip)[source]: Adjust patches accordingly.

gnu/packages/patches/unzip-CVE-2015-7696.patch

@@ -0,0 +1,35 @@
+Copied from Debian.
+
+From: Petr Stodulka <pstodulk@redhat.com>
+Date: Mon, 14 Sep 2015 18:23:17 +0200
+Subject: Upstream fix for heap overflow
+Bug-Debian: https://bugs.debian.org/802162
+Bug-RedHat: https://bugzilla.redhat.com/show_bug.cgi?id=1260944
+Origin: https://bugzilla.redhat.com/attachment.cgi?id=1073002
+Forwarded: yes
+
+---
+ crypt.c | 12 +++++++++++-
+ 1 file changed, 11 insertions(+), 1 deletion(-)
+
+--- a/crypt.c
++++ b/crypt.c
+@@ -465,7 +465,17 @@
+     GLOBAL(pInfo->encrypted) = FALSE;
+     defer_leftover_input(__G);
+     for (n = 0; n < RAND_HEAD_LEN; n++) {
+-        b = NEXTBYTE;
++        /* 2012-11-23 SMS.  (OUSPG report.)
++         * Quit early if compressed size < HEAD_LEN.  The resulting
++         * error message ("unable to get password") could be improved,
++         * but it's better than trying to read nonexistent data, and
++         * then continuing with a negative G.csize.  (See
++         * fileio.c:readbyte()).
++         */
++        if ((b = NEXTBYTE) == (ush)EOF)
++        {
++            return PK_ERR;
++        }
+         h[n] = (uch)b;
+         Trace((stdout, " (%02x)", h[n]));
+     }