ykpers 1.6.4
ykpers 1.6.4

Upgrade ykpers to version 1.6.4.
Add `--disable-dependency-tracking`.
Add `--with-backend=osx` to be explicit because that's the default
backend and because it might use `libusb`, and it's likely better
to be consistent across all installs by using the native osx BE.
Tested against the recent libyubikey-1.9 on Lion using clang and
llvm from XCode-4.3.3.

Signed-off-by: Adam Vandenberg <34c2b6407fd5a10249a15d699d40f9ed1782e98c@gmail.com>

sakra/homebrew,sakra/homebrew,sakra/homebrew,sakra/homebrew