python: 2.7.3 -> 2.7.4
perl: remove one more unreliable test, fixes #454
Switch stdenv to GCC 4.8.0.
gmp-4.3.2.nix: disable test suite to fix the build

The test t-lucnum_ui fails (on Linux/x86_64) when built with GCC 4.8.
Newer versions of GMP don't have that issue anymore.
guile: disable test suite to fix build

  ERROR: socket.test: AF_INET6/SOCK_STREAM: bind - arguments: ((system-error "bind" "~A" ("Cannot assign requested address") (99)))
  ERROR: socket.test: AF_INET6/SOCK_STREAM: bind/sockaddr - arguments: ((system-error "bind" "~A" ("Cannot assign requested address") (99)))
iproute: don't compile with -Werror

  lnstat.c:169:30: error: argument to 'sizeof' in 'memset' call is the same expression as the destination; did you mean to provide an explicit length? [-Werror=sizeof-pointer-memaccess]
     memset(th.hdr[i], 0, sizeof(th.hdr[i]));
                                ^
  cc1: all warnings being treated as errors
  make[1]: *** [lnstat.o] Error 1
elfutils: disable -Werror to fix the build

  nm.c: In function 'show_symbols_sysv':
  nm.c:773:27: error: argument to 'sizeof' in 'snprintf' call is the same expression as the destination; did you mean to provide an explicit length? [-Werror=sizeof-pointer-memaccess]
      snprintf (name, sizeof name, "[invalid sh_name %#" PRIx32 "]",
                             ^
  cc1: all warnings being treated as errors
grub: fix download URL for grub-0.97-once.patch
release-small.nix: drop the Emacs 23.x packages from this file

Most of these packages are very old and don't compile in 'master' to
begin with, so it's probably not necessary to use them for testing the
stdenv-updates branch.
release-small.nix: switch Emacs 23 to 24
flac: update download URL for build fix patch
libgdiplus: fix download URL for 'libgdiplus-2.10.1-libpng15.patch'
bup: update to version 0.25-rc1-107-g96c6fa2 and drop -Werror to fix the build

  /nix/store/4jfqcb4mzh3vl08zgfh9ir46jii7rcb9-python-2.7.3/include/python2.7/modsupport.h:27:1: error: 'PyArg_ParseTuple' is an unrecognized format function type [-Werror=format=]
   PyAPI_FUNC(int) PyArg_ParseTuple(PyObject *, const char *, ...) Py_FORMAT_PARSETUPLE(PyArg_ParseTuple, 2, 3);
   ^
  cc1: all warnings being treated as errors
aterm-2.8: add comment about build failures with gcc 4.8.x
squid: build without -Werror to fix build on GCC 4.8.x