libvpx: Pull from upstream

source/libvpx/README

 vpx Multi-Format Codec SDK
 README - 1 August 2013
 
 Welcome to the WebM VP8/VP9 Codec SDK!
 
 COMPILING THE APPLICATIONS/LIBRARIES:
   The build system used is similar to autotools. Building generally consists of
   "configuring" with your desired build options, then using GNU make to build
   the application.
 
   1. Prerequisites
 
     * All x86 targets require the Yasm[1] assembler be installed.
     * All Windows builds require that Cygwin[2] be installed.
-    * Building the documentation requires PHP[3] and Doxygen[4]. If you do not
-      have these packages, you must pass --disable-install-docs to the
-      configure script.
-    * Downloading the data for the unit tests requires curl[5] and sha1sum.
+    * Building the documentation requires Doxygen[3]. If you do not
+      have this package, the install-docs option will be disabled.
+    * Downloading the data for the unit tests requires curl[4] and sha1sum.
       sha1sum is provided via the GNU coreutils, installed by default on
       many *nix platforms, as well as MinGW and Cygwin. If coreutils is not
       available, a compatible version of sha1sum can be built from
-      source[6]. These requirements are optional if not running the unit
+      source[5]. These requirements are optional if not running the unit
       tests.
 
     [1]: http://www.tortall.net/projects/yasm
     [2]: http://www.cygwin.com
-    [3]: http://php.net
-    [4]: http://www.doxygen.org
-    [5]: http://curl.haxx.se
-    [6]: http://www.microbrew.org/tools/md5sha1sum/
+    [3]: http://www.doxygen.org
+    [4]: http://curl.haxx.se
+    [5]: http://www.microbrew.org/tools/md5sha1sum/
 
   2. Out-of-tree builds
   Out of tree builds are a supported method of building the application. For
   an out of tree build, the source tree is kept separate from the object
   files produced during compilation. For instance:
 
     $ mkdir build
     $ cd build
     $ ../libvpx/configure <options>
     $ make
@@ skipping 89 matching lines @@
 
   5. Configuration errors
   If the configuration step fails, the first step is to look in the error log.
   This defaults to config.log. This should give a good indication of what went
   wrong. If not, contact us for support.
 
 SUPPORT
   This library is an open source project supported by its community. Please
   please email webm-discuss@webmproject.org for help.