Fix/Enable build for 64-Bit Matlab on OSX 10.9

* Update rapidxml_print.h with a copy from Horde3D's git mster, which contains
  required build fixes for building with gcc-4.9+ or clang.

  See commit in Horde3D:

  https://github.com/horde3d/Horde3D/commit/104a6f6f3b41d36b8cf7a7267fbda768efb85f07

* Add our special mexopts.sh Matlab options file to allow building a mex file
  on 10.9 with 10.9 SDK which is backwards compatible to OSX 10.6+ Snow Leopard
  and later.

* Modify makeHorde.m build script to enable 64-Bit Matlab for OSX builds.
  64-Bit Octave on OSX is not yet working.
Add support for 64-Bit Matlab on OSX 10.6 and later.

New subfolder HordeOSX64/ contains the mex file and the
Horde3D and Horde3DUtils frameworks which need to be
installed on the target machine.

Recommended install location for the .framework folders is
/Library/Frameworks/

-> Built and tested on OSX 10.9 with R2012a 64-Bit.