Unpatched security vulnerabilities in GNU IceCat

[Mark H Weaver <mhw@netris.org>]

I've pushed an update to the GNU IceCat 31.8 package in GNU Guix that
fixes some of the security vulnerabilities fixed upstream in Firefox ESR
38.2, listed here:

  https://www.mozilla.org/en-US/security/known-vulnerabilities/firefox-esr/

Unfortunately, I was not able to backport all of the fixes mentioned
there, because some of the underlying code has changed dramatically
between versions 31 and 38.  Specifically, I was unable to address the
following issues:

(the commit IDs below are for the 'gecko-dev' git mirror)

* https://www.mozilla.org/en-US/security/advisories/mfsa2015-90/
  (CVE-2015-4487) (mozilla bug 1171603).  Although the advisory claims
  that it's fixed in ESR 38.2, I was unable to find any commit
  mentioning bug 1171603 on the esr38 branch.  However, I did find
  commits b6e7f5efcf6ff0307b0b3def8d037621e76f920d and
  52ee71547cdcbf7c0da5df53c5182f623d9df384 on their master branch.
  I can probably backport these with some effort, but ran into
  difficulties in my initial attempt.

* https://www.mozilla.org/en-US/security/advisories/mfsa2015-87/
  (CVE-2015-4484) (mozilla bug 1171540).  The underlying code has
  changed radically and I have no idea how to proceed.  Upstream
  commit 6e1f2aeeaedc1042bce1983552cd38169edef38e.

* https://www.mozilla.org/en-US/security/advisories/mfsa2015-82/
  (CVE-2015-4478) (mozilla bug 1105914).  I was unable to find any
  commit in the upstream repository that's tagged with this bug.

* https://www.mozilla.org/en-US/security/advisories/mfsa2015-79/
  (CVE-2015-4473) (mozilla bugs 1182711, 1146213, 1178890).  I was able
  to backport the fix for bug 1178890, but I was unable to backport the
  other two, which are fixed in upstream commits
  2edecbf4333665b8fad36b94069d780cde4de908 and
  f1c0791994791a94e065aa1755bd96b34dc7b7dc.

I don't expect anyone to fix these problems in version 31, so we're
probably stuck until GNU IceCat 38.x is released.  Hopefully that will
be soon.

If anyone would like to attempt to backport the missing bits above,
please let me know!

      Mark