silk_sources.mk no longer needs to be patched (s/if/ifdef/) for
the draft Makefile to work.

commit 5b64cf7c4d67af9050bc959996ef976ce6326888
Author: Jean-Marc Valin <jean-marc.valin@octasic.com>
Date:   Thu May 19 16:40:35 2011 -0400

    Fixes a few bugs introduced in the latest update

commit b91eb86025d2de3c4cf04f4fb1aa48a28ad676a3
Author: Timothy B. Terriberry <tterribe@xiph.org>
Date:   Thu May 19 16:12:02 2011 -0400

    build_draft.sh fixes

commit 0b10c30db7ad60ff7d4bfc1139bdb86e0543c035
Author: Jean-Marc Valin <jean-marc.valin@octasic.com>
Date:   Thu May 19 15:30:21 2011 -0400

    Fixes the draft build

commit 164424cded5978e657105104e171ac202dde5e5b
Author: Jean-Marc Valin <jean-marc.valin@octasic.com>
Date:   Thu May 19 15:00:23 2011 -0400

    Updated build system

commit 188d9fcba8c3a1b1ad67c67c430e1b37e3658a40
Author: Koen Vos <koen.vos@skype.net>
Date:   Thu May 19 17:14:57 2011 -0400

    SILK/Opus update

This also includes changes to build_draft.sh to allow it to be
 invoked from anywhere.