Re-License LIBXC under LGPL

From Ian Campbell:
As previously discussed we would like to relicense libxc under the LGPL.
https://xenproject.org/index.php/2010/07/26/xen-org-source-code-license-change-request/
http://lists.xensource.com/archives/html/xen-devel/2010-07/msg01378.html
We have now managed to track down all but one of the necessary contributors in order to make this change and all have given their OK to the change.
Due to the missing contributor (who we do not expect we will be able to find) we have taken the decision to remove the xc_ptrace functionality. It is currently unused, the last remaining user having been replaced by gdbsx. Should this code be required in the future it can be recovered from mercurial history and reinstated as a separate library.
There are two patches currently in review on xen-devel for this final change.