Fix compilation warning when building for arm64

When building for arm64, NSInteger is a 64-bit value. Recommendations
are to either use "%ld" and cast the value to long or to use "%zd".
This patch uses "%zd" that work on both armv7 and arm64 as it avoid
doing a cast.

DELTA=1  (0 added, 0 deleted, 1 changed)

git-svn-id: http://google-toolbox-for-mac.googlecode.com/svn/trunk@658 7dc7ac4e-7543-0410-b95c-c1676fc8e2a3