Mavericks build fixes.
Use xcrun to get SDK path, if available
Occasionally the kextutil freak out and claim unrelated bundles are needed,
like that of com.apple.driver.AppleIntelSNBGraphicsFB. Lets not make
such things be a build failure.
If hostid is unset (default) generate a hostid from kern.uuid (FNV-1a)
Alas, kern.uuid is simply the kernel build uuid, as is the same across
systems. Remove the hostid code, and bring logic into ZFS.

https://github.com/zfs-osx/zfs/commit/b20c279a63b96865f8ce9de3f4b0f3fc95148aea
Remove the initialised debugging code as we are fairly stable with the
mutex code.
Make rwlock use own lck_grp
Clean up all warnings
Aligned mutex struct after removing initialized member
Change to use zones for allocations, to avoid running out.
Add the kernel dependency hack kext to SPL instead of ZFS.
Cleanup condvars to ignore waiters.
Fix zone names, and gather more statistics
Add more sysctl, and counters, fix missing 1024 entry.
total was counted twice, kmem_used() was returning available, added
kmem_avail().
Some hack'n'slashery
Base available memory on actual kernel limitations, and allow zsize adjustment.
Make sure to obey KM_NOSLEEP in kmem_alloc.
If 'zsize' is used, clamp it to no more than 50% of memory.
"kmem_alloc" alternate branch to test more direct allocations.
Remove kerneldependencies we no longer need.
No longer retry allocations.
"PlugIns" directory is case sensitive.
Clean up, take out zones code, remove un-needed sysctls and
malloc retry.
Merge branch 'master' of https://github.com/zfs-osx/spl