Added cast to fix warning on 32-bit builds.

The call to memcpy in -dataForColumnIndex: was being passed an int (it accepts a size_t, ie: long on some platforms). This generated a warning in Xcode 5 when building (in my instance) for the iPad.
Merge pull request #271 from aryounce/patch-1

Added cast to fix warning on 32-bit builds.
Merge branch 'master' of git://github.com/ccgus/fmdb