Add a SPL_AC_TYPE_ATOMIC64_T test to configure for systems which do

Add a SPL_AC_TYPE_ATOMIC64_T test to configure for systems which do
already supprt atomic64_t types.

* spl-07-kmem-cleanup.patch
This moves all the debugging code from sys/kmem.h to spl-kmem.c, because
the huge macros were hard to debug and were bloating functions that
allocated memory. I also fixed some other minor problems, including
32-bit fixes and a reported memory leak which was just due to using the
wrong free function.

git-svn-id: https://outreach.scidac.gov/svn/spl/trunk@163 7e1ea52c-4ff2-0310-8f11-9dd32ca42a1c