build system: fix 32 bit build on Snow Leopard

build system: fix 32 bit build on Snow Leopard
gcc-4.2 on SL reports i686 (but generates x86_64 code by default)
and uname -m reports i386 (unless you hold 6+4 keys while booting)
so modify configure.py to always add '-arch xxx' option on os x

Also, update libtheora to svn 16547 since the 1.0 release doesn't compile
on SL.

git-svn-id: svn://localhost/HandBrake/trunk@2800 b64f7644-9d1e-0410-96f1-a4d463321fa5