Switch back to rpetrich's theos fork for now, but keep substrate generator.
Something is broken with the armv6 binaries that Xcode6 is generating using the technique from
http://iphonedevwiki.net/index.php/Updating_extensions_for_iOS_7 - I suspect it may be the
compiler's fault.

Revert "Switch back to DHowett's theos and substrate generator"

This reverts commit c2f74e8b261e1e085bc4db1d8abde95e2c86365d.