gnu: libwmf: Add fixes for several security flaws.

gnu: libwmf: Add fixes for several security flaws.

* gnu/packages/patches/libwmf-CAN-2004-0941.patch,
  gnu/packages/patches/libwmf-CVE-2007-0455.patch,
  gnu/packages/patches/libwmf-CVE-2007-2756.patch,
  gnu/packages/patches/libwmf-CVE-2007-3472.patch,
  gnu/packages/patches/libwmf-CVE-2007-3473.patch,
  gnu/packages/patches/libwmf-CVE-2007-3477.patch,
  gnu/packages/patches/libwmf-CVE-2009-3546.patch: New files.
* gnu/packages/patches/libwmf-CVE-2015-0848+4588+4695+4696.patch: Delete
  file.  Replace with ...
* gnu/packages/patches/libwmf-CVE-2015-0848+CVE-2015-4588.patch,
  gnu/packages/patches/libwmf-CVE-2015-4695.patch,
  gnu/packages/patches/libwmf-CVE-2015-4696.patch: ... these new files.
* gnu-system.am (dist_patch_DATA): Adjust accordingly.
* gnu/packages/image.scm (libwmf)[source]: Adjust set of patches.